Driving method for a liquid crystal display device

ABSTRACT

A driving method for a direct addressing type liquid crystal display device for displaying gradation by changing the amplitude of voltages applied to pixels, wherein a series of voltage pulses, as signal voltages, composed of a plurality of different voltage levels are applied in order to display a specified gradation, and for a display, a plurality kinds of gradation in which a part of the voltage levels is commonly used are selected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving method for a passiveaddressing type liquid crystal display device.

2. Discussion of the Background

As a basic driving method for a passive (multiplexed) addressing typeliquid crystal display element, there has been proposed a linesuccessive selection method (for instance, APT: Alt Pleshko Technique)or IAPT (Improved Alt Pleshko Technique as an improvement of APT). Thistechnique is very useful as a multiplex driving method since ON-OFFlevels can be easily driven. However, since the direct addressing typeliquid crystal display device does not use active elements such as TFTs,there was a problem of reduction of contrast ratio due to frame responsewhen a liquid crystal display element of fast response was used.

In order to solve such problem, a multiple line selection method hasbeen proposed whereby it has been possible to display a picture having ahigh contrast ratio at a high speed. Further, in order to achieve thesame purpose as described above, an attempt of using a whole linesimultaneous selection method (AA: Active addressing) has been reported.Thus, a new addressing technique has been developed with the result ofimproving a quality of display.

There has been an increased demand for displaying pictures with manygradation levels for personal computers, TVs etc. and liquid crystaldisplay devices as well. Several methods have been used for displayswith gradation. In an active type driving method using transistors,diodes, or the like, an amplitude modulation can be easily achieved byusing voltage pulses whose pulse height is varied depending on gradationlevels of data to be displayed. This is because voltages applied toliquid crystal are basically of a static waveform.

In a passive multiplexed type driving method which typically uses a STN(super-twisted nematic) liquid crystal element and so on, however, thereis a voltage change in a non-selection time when voltage pulses whosepulse height is varied depending on gradation levels of data to bedisplayed are simply applied to the element. Under the circumstances,there have been used or proposed several methods to display gradationlevels in the passive multiplexed type driving method.

In the conventional driving methods of driving STN, there have beenproposed and used a frame rate control method (FRC) and a pulse widthmodulation method (PWM) in order to obtain a display with gradation.Recently, an amplitude modulation method (AM) has been proposed. In thefollowing, description will be made briefly on the proposed methods, andthen, description will be made on problems caused when these methods areapplied to the multiple line selection method.

(1) Frame rate control (FRC)

A gradation display is made with use of a plurality of frames. Namely,an intermediate tone is formed in response to the number of ON and OFFas a binary state. For instance, when three frames are used, fourstates, ON/ON/ON, ON/OFF/ON, OFF/ON/OFF and OFF/OFF/OFF can bedisplayed.

However, when a picture having many gradation levels is to be displayedwith use of the FRC method, there may cause a flicker because anincreased number of frames takes a long time to complete a display.Practically, the FRC method is combined with a spatial modulation methodfor shifting spatially phases to thereby avoid the occurrence of theflicker. However, the proposed method is considered to be difficult toobtain a picture having more than 16 gradation levels.

Another important problem in the FRC method resides in difficulty inapplying it to a video display. For instance, in a display of dynamicpicture, the display should be completed in a period in which a dynamicpicture is changed. Accordingly, it is impossible to use many frames,and a display of many gradation levels is difficult.

For instance, when a frame frequency of 120 Hz (a generally usedfrequency, and the length of a frame is 8.3 ms) is used and a dynamicpicture of 30 pictures per sec.(30 Hz) is to be displayed, it isnecessary to complete the display in 4 frames. In this case, the numberof gradation levels which can be displayed is only about 5 to 8. Thus,the FRC method was insufficient to display a dynamic picture having manygradation levels.

(2) Pulse width modulation (PWM)

In this method, a selection time period is divided into, for instance, a2^(n) number of sub-periods, and an ON state and an OFF state aredistributed to the sub-periods. This method can be considered as such atechnique that the FRC method is carried out in a frame. However, thismethod has a drawback that ununiformity becomes large in a display asthe density and the gradation levels of a display is increased becausethe driving frequency is increased in proportion to the number ofdivided time periods.

(3) Amplitude modulation (AM)

As described before, it is impossible to multiplexed driving the passiveaddressing type LCD by simply applying voltage pulses whose pulse heightis varied depending on gradation levels of data to be displayed, and itis necessary to avoid a change of the effective voltage to pixels in anon-selection time. For this purpose, there have been proposed twotechniques: application of a plurality of voltages and use of animaginary electrode.

In the former technique, different data (column) voltages are applied totwo or more frames, or a selection time period is divided into two ormore time periods wherein different data voltages are applied to thedivided time periods. The application of a plurality of voltages makesthe effective voltage in a non-selection time constant whereby a desiredgradation display can be obtained. Specifically, the voltagescorresponding to two kinds of data as shown in Formula 1 may be appliedto each frame, or the two kinds of voltages may be applied by exchangingthem in a selection time period.

Formula 1

    d+(1-d.sup.2).sup.0.5

    d-(1-d.sup.2).sup.0.5

where d indicates display data (ON: -1, OFF: 1)

Hereinbelow, the data shown in Formula 1 are referred to as divideddata. The application of only part of the divided data does not renderthe effective voltage value to be a predetermined constant value, andtherefore, addressing is not completed. Accordingly, in a case that thedivided data are applied to each of the frames, the frames are referredto as subframes in order to distinguish them from the ordinary frames.

The divided data are featurized by including components which varydepending on gradation levels of data. However, since the divided datarespectively include a correction term, (±(1-d₂)⁰.5), the effectivevalue of voltages applied to pixels in a non-selection time can be keptconstant. New divided data can be produced on the basis of therespective divided data, whereby more than two kinds of divided data canbe used.

In this technique, a device capable of supplying a plurality of voltagelevels is required. In order to display K gradation levels, voltages ofa (2K-2) number of levels are required. Namely, a display of 8 gradationlevels requires 14 voltage levels. As the number of gradation levelsincreases, the number of voltage levels increases. An increased numberof voltage levels will cause an increased manufacturing cost. Further, astate of display is basically determined by applying two voltage levels.Accordingly, if a time interval of applying a unit voltage (a width ofpulses of a voltage) is made constant, the length of frames forcompleting a display is twice as in the conventional technique.

Another method of avoiding a change of the effective voltage values tonon-selected pixels is to provide at least one line of imaginaryelectrode, wherein selection lines are driven so as to display data forthe imaginary row electrode, or voltage levels which have been imaginarydetermined may be applied to the selection lines. This method had anadvantage that there is no substantial change in frequency because thelength of frame is not made double. However, this method hasdisadvantages that operations with all line data are necessary, and thenumber of voltage levels to be supplied is remarkably increased due tothe sum of the number of gradation levels and the number of correctionlevels. In particular, the increase of the number of voltage levels is aserious problem which has prevented the spreading of the AM method. Theabove-mentioned two methods include a technique referred in U.S. Ser.No. 08/098,812 and a technique referred to as a pulse height modulation(PHM) disclosed in Japanese Unexamined Patent Publication No. 89082/1994(or EP 569974).

As described above, the technique for displaying gradation with use ofthe amplitude modulation method inevitably caused a complicated circuitstructure and the necessity of using drivers for a number of levels,which invited a substantial increase of manufacturing cost.

(4) Problems in multiple line selection method

In the multiple line selection method, the above-mentioned conventionaldriving method can be utilized with a certain modification. Forinstance, when a gradation display is conducted in accordance with theamplitude modulation method in addition to using a plurality of divideddata, each of the divided data is displayed in accordance with themultiple line selection method whereby a gradation display is possible.Namely, column signals are formed by the orthogonal transformation ofthe divided data with use of a predetermined selection matrix (anorthogonal matrix).

However, the before-mentioned problem on the gradation display equallytakes place in the multiple line selection method. The frequency ratecontrol method (FRC) and the pulse width modulation method (PWM) havethe same problem as the successive line selection method concerning thedifficulty of obtaining a display having a number of gradation levels.In the amplitude modulation method, an increase of the maximum voltagevalue and an increased number of voltage levels due to selectingsimultaneously a plurality of lines cause more serious problem incomparison with the successive line selection method. In other words, inthe multiple line selection method, calculation with use of anorthogonal function is needed whereby a large number of voltage levelsare necessary for display. Further, the construction of circuit iscomplicated. An increased number of gradation levels causes a bigproblem of pushing up manufacturing cost.

The multiple line selection method utilizing the amplitude modulationmethod requires a large number of voltage levels even though the numberof gradation levels is small and the number of lines simultaneouslyselected is small. For instance, in a case that the number of gradationlevels to be displayed by the AM method is only 8 and each line issuccessively selected, 12 voltage levels are needed because 6 gradationlevels in 8 gradation levels are used for data of intermediate values,and it is necessary to provide voltage levels as twice as the number ofdata for the intermediate values even in a case that each line issuccessively selected. In the application of the AM method to themultiple line selection method wherein addition and subtraction ofvoltage levels are conducted at the time of the orthogonaltransformation, the number of voltage levels is fairly increased eventhough the number of simultaneously selected lines is small. Forinstance, when L (the number of simultaneously selected lines)=3,voltage levels of about 8³ =512 are required. Namely, the amplitudemodulation in the multiple line selection method requires column driversof a very high degree of resolution (more than 8 bits, preferably 10-12bits). If drivers having a smaller number of levels are used, thereproduces data error.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the disadvantagesin the conventional methods which require a large number of voltagelevels in comparison with an amount of information of gradation and toprovide a driving method for a liquid crystal display device capable ofefficiently supplying information and providing a correct gradationdisplay.

In accordance with the present invention, there is provided a drivingmethod for a liquid crystal display device using a multiplex drivingmethod which comprises:

(a) in a display of gradation data, applying to pixels a plurality ofvoltage pulses including components, in the respective pulse heights,which vary depending on gradation levels of data to be displayed,whereby RMS voltages applied to pixels on scanning electrodes in anon-selection state are effectively made constant in a display frameperiod, and

(b) using a part of the plurality of voltage pulses commonly in at leasttwo data of different gradation level used for display, whereby thenumber of pulse heights of the voltage levels necessary for display isreduced.

Further, the present invention is to provide a driving method for aliquid crystal display device using a multiplex driving method whichcomprises:

(a) in a display of gradation data, applying to pixels voltage pulseshaving pulse heights which correspond to a plurality of gradation data(divided gradation data) including components which vary depending ongradation levels of data to be displayed, whereby RMS voltages appliedto pixels on scanning electrodes in a non-selection state areeffectively made constant in a display frame period, and

(b) using a part of the plurality of divided gradation data commonly inat least two different gradation data used for display.

Further, in any of the above-mentioned driving methods, gradation dataare displayed in association with a frame modulation or a pulse widthmodulation.

Also, in the above-mentioned methods, a plurality of scanning electrodesare simultaneously selected. In particular, when an intermediategradation data are displayed, signals which are applied to the dataelectrodes in response to selection pulses in a time period wherein allthe scanning electrodes are applied with at least one selection pulseinclude in a mixed state at least one signal which is obtained by theorthogonal transformation of a data element having the absolute valueexceeding 1 among the divided gradation data and at least one signalwhich is obtained by the orthogonal transformation of a data elementhaving the absolute value less than 1.

Further, in particular, when an intermediate gradation data aredisplayed, signals which are applied to the data electrodes in responseto selection pulses applied once to a simultaneously selected scanningelectrode group include in a mixed state at least one signal which isobtained by the orthogonal transformation of a data element having theabsolute value exceeding 1 among the divided gradation data and at leastone signal which is obtained by the orthogonal transformation of a dataelement having the absolute value less than 1.

Further, in the method firstly and secondly mentioned, a plurality ofscanning electrodes are simultaneously selected, and when signals areapplied to the data electrodes with respect to a simultaneously selectedscanning electrode group, the signals are formed by the orthogonaltransformation of all the divided gradation data necessary fordisplaying a predetermined gradation data, and the signals aresuccessively applied as a group for each of column vectors of theselection matrix, to the data electrodes in response to a timing of theapplication of the selection pulses.

In the above-mentioned methods, a plurality of scanning electrodes aresimultaneously selected, and at least one imaginary scanning electrodeis added to the simultaneously selected scanning electrodes, and dataare determined for the imaginary scanning electrode so that the numberof voltage levels to be applied to data electrodes is reduced.

In particular, in any of the above-mentioned driving methods, thedisplay data corresponding to the simultaneously selected scanningelectrodes (which include at least one imaginary scanning electrodes)are divided into plural groups of display data having different absolutevalues; and data are determined for the imaginary scanning electrodes sothat the number of display data included in each of the groups takes apredetermined discrete integer value. Or, the product of the columnvector elements in the selection matrix takes a predetermined sign, anddata are determined for the imaginary scanning electrodes so that theproduct of the display data elements corresponding to the simultaneouslyselected scanning electrodes (which include at least one imaginaryscanning electrode) takes a predetermined sign.

The present inventions provides the following effects.

1) A liquid crystal display device of multi-gradation can be driven withdrivers of a practical number of voltage levels (64-32 levels or lower).Namely, remarkable simplification to a circuit system and reduction ofmanufacturing cost can be achieved in comparison with the conventionaltechnique.

2) A completely independent display is obtainable without data error. Apicture image of high quality can be provided without any specialtreatment to the data. Namely, a picture image free from data error suchas crosstalk can be provided.

In the present invention, when gradation is displayed by changing theamplitude of voltages, a series of voltage pulses composed of aplurality of different voltage levels are applied, as signal voltages,in order to display a specified gradation, whereby a change of theeffective voltages to be applied to non-selected pixels is prevented. "Aplurality of voltage levels" can be determined by various methods.

First, a display data is expressed by a plurality of data, i.e., divideddata. A specified gradation can be displayed by displaying the divideddata. In a multiple line selection method, column signals are formed bythe orthogonal transformation of the data to be displayed. In this case,the order of the division of the data and the orthogonal transformationof the data can be exchanged. In other words, the divided column signalsmay be formed by forming the divided data before the orthogonaltransformation of the divided data. Or, the data to be displayed aresubjected to the orthogonal transformation to thereby form the columnsignals, and then, the column signals may be expressed with a pluralityof divided column signals.

Further, a single correction column signal may be applied forsimultaneously selected lines. In this case, the correction columnsignals may be treated as data on an imaginary line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing voltage values to be applied to pixels withrespect to various row waveforms and column waveforms in a combinationof d₁ =0.6 and d₂ =0.8 according to the present invention;

FIG. 2 is a diagram showing the effect of reducing voltage levels in acase that a driving method for selecting simultaneously two lines isused and a single line of imaginary electrode is added;

FIG. 3 is a diagram showing the effect of reducing voltage levels in acase that a driving method for selecting simultaneously three lines isused and a single line of imaginary electrode is added;

FIG. 4 is a block diagram of a circuit used for a multiple lineselection method on the present invention;

FIG. 5 is a block diagram showing a circuit for practicing the presentinvention;

FIG. 6a is a diagram showing memory mapping for practicing aconventional technique;

FIG. 6b is a diagram showing memory mapping for practicing the thepresent invention;

FIG. 7 is a circuit diagram of an embodiment of a gradation datatransforming circuit in FIG. 5;

FIG. 8 is a block diagram of an embodiment of a circuit in an integratedform used for practicing the present invention;

FIG. 9 is a block diagram of another embodiment of a circuit in anintegrated form for practicing the present invention; and

FIG. 10 is a diagram showing an idea of memory management for practicingthe present invention.

DISCUSSION OF THE PREFERRED EMBODIMENTS

The present invention is to propose an amplitude modulation (AM) typegradation driving method by which a much increase of the number ofvoltage levels necessary to the number of gradation levels is avoidableand a gradation display is effected with the number of voltage levels inminimum requirement.

The present invention is applicable to all kinds of AM methods. The AMmethods include a method as disclosed in U.S. Ser. No. 08/098,812 filedby the applicant of this application and a method as in EP 569974. Thetwo methods propose some solutions in the infinite number of solutionsin the AM methods. Namely, a method of displaying gradation data byapplying to pixels a plurality of voltage pulses including components,in the respective crest values, which vary depending on gradation levelsof data to be displayed, is expressed by the following conditions.

In a case that an L (more than or equal to 1) number of scanningelectrodes are simultaneously selected, and an orthogonal functionsignals A Ami! (where Ami are elements, i.e., 1, -1 and 0, in m rows andi columns in the orthogonal matrix A; m is an integer of 1-L, and i isan integer of 1-M, which corresponds to the i th selection signal in adisplay cycle) are used as signals applied to the selected scanningelectrodes, and when there is (C₁, C₂, . . . , C_(M))=(d₁, d₂, . . . ,d_(L)) A to obtain predetermined gradation level d_(j) (d_(j) takes avalue between 1 indicating OFF and -1 indicating ON depending ongradation levels) with respect to the pixel on the j th (j is an integerof 1-L) line in a simultaneously selected group of electrodes concerninga specified column, the column is substantially applied with a voltagein proportion to two kinds of voltages expressed by the followingFormula 2:

Formula 2

    X.sub.i =C.sub.i +(q.sub.i -C.sub.i.sup.2).sup.1/2

    Y.sub.i =C.sub.i -(q.sub.i -C.sub.i.sup.2).sup.1/2

where Σq_(i) =constant≧tr ^(t) AA! (where t indicates the transpositionof the matrix, and tr ! indicates the sum of diagonal components in thematrix of ! ).

The method disclosed in U.S. Ser. No. 08/098,812 by the applicant is acase that Σq_(i) =tr ^(t) AA!, and q_(i) is equal to all i. In methodsdisclosed in EP 569974, the method called "Split interval mode" is suchthat q_(i) is determined with change of i in order to meet the gradationdisplay method using a pulse width modulation method. In these methods,voltage pulses having different values are used.

Although, the present invention is widely applicable to all AM methods,a driving method using two levels in Formula 1 will be exemplified forsimplification of explanation.

In the successive line selection method (or APT method), a display ofspecified gradation levels can effectively be expressed by adding twolevels as described in Formula 1.

In the present invention, a plurality of gradation levels are expressedwith use of the same level elements so that the number of voltage levelsused can be reduced as a whole. The idea of the present invention isthat gradation levels having special values are selected for display. Onthe contrary, the idea of the conventional technique is that gradationlevels are determined based on the bit number of input signal and aspecification of treating circuits. Namely, if a part of divided data oftwo different display data is commonly used, the number of voltagelevels required is not increased so much. For instance, when two sets ofdisplay data (±d₁, ±d₂) are added to display gradation levels other thanON, OFF and 50% gray (which can be expressed by ON+OFF), and the numberof voltage levels required must not be increased beyond the number ofgradation levels increased, the condition described in Formula 3 shouldbe satisfied. From Formula 3, the condition of Formula 4 is introduced.

Formula 3

    |d.sub.1 +(1-d.sub.1.sup.2).sup.0.5 |=|d.sub.2 +(1-d.sub.2.sup.2).sup.0.5 |

Formula 4

    d.sub.1.sup.2 (1-d.sub.1.sup.2).sup.0.5 =d.sub.2.sup.2 (1-d.sub.2.sup.2).sup.0.5

wherein d₁ ≠d₂

In Formula 4, d₁ and d₂ are expressed by the square of the data valuesand are symmetrical with respect to positive and negative signs.Accordingly, the four gradation levels of ±d₁, ±d₂ can be displayed byadding four voltage levels. Table 1 shows an example of the pair of d₁and d₂.

                  TABLE 1    ______________________________________    d.sub.1         0.2      0.3      0.4    0.5    0.6  0.7    d.sub.2         (0.96).sup.0.5                  (0.91).sup.0.5                           (0.84).sup.0.5                                  (0.75).sup.0.5                                         0.8  (0.51).sup.0.5    ______________________________________

When a certain gradation data d₁ (and -d₁) is used, d₂ (=(1-d₁ ²)⁰.5) isused as the partner of d₁, whereby the number of required voltage levelscan be made the same as the increased number of gradation levels. Suchcombination of gradation levels can not generally be obtained based on aconventionally used display using 8 gradation, 16 gradation, 32gradation or the like.

In the conventional technique, the pulse heights corresponding togradation levels do not coincide, and when they are driven by drivershaving a smaller number of voltage levels, there is a high possibilityof data errors.

In accordance with the method of the present invention, the number oflevels required with respect to the number of gradation levels K isexpressed by Formula 5.

Formula 5

    (K-2)+2=K

Accordingly, reduction in the number (K-2) levels is possible incomparison with the conventional system requiring (2K-2) levels.Incidentally, with use of a voltage level of ±1, data "0" (50% gray) canbe displayed.

As described before, a display can be completed by displaying thedivided display data with two subframes. As the display data displayedby using the amplitude modulation method, there are provided ON (d=-1),OFF (d =+1), 50% gray (d=0), (however, d=0 is not essential in thepresent invention), and four data are selected so as to satisfy thecondition of Formula 4. Namely, it consider that ±1, ±d₁ and ±d₂(=±(1-d₁ ²)⁰.5) (and 0) are used as gradation levels. In this case, twodivided data necessary to express each of the display data are shown inTable 2 where the meaning of X₀ and Y₀ are shown in Formula 6.

                  TABLE 2    ______________________________________    Display data  Divided data 1                             Divided data 2    ______________________________________    1             1          1    d.sub.1       X.sub.0    Y.sub.0    d.sub.2       X.sub.0    -Y.sub.0    0             1          -1    -d.sub.2      Y.sub.0    -X.sub.0    -d.sub.1      -Y.sub.0   -X.sub.0    -1            -1         -1    ______________________________________

Formula 6

    X.sub.0 =d.sub.1 +(1-d.sub.1.sup.2).sup.0.5

    Y.sub.0 =d.sub.1 -(1-d.sub.1.sup.2).sup.0.5

The order of applying the two divided data may be exchanged, whereby ±1and ±X₀ are used as the divided data for a subframe, and ±1 and ±Y₀ areused as the divided data for the other subframe. In this case, thesubframe using ±1 and ±X₀ is referred to as an X subframe; the divideddata used for the X subframe is referred to as divided data X; thesubframe using ±1 and ±Y₀ is referred to as a Y subframe, and thedivided data used for the Y subframe is referred to as divided data Y.In this case, the divided data X and Y to show each of the display dataare as shown in Table 3. From the definition, X₀ has an absolute valueof more than 1 and Y₀ has an absolute value of lower than 1.

                  TABLE 3    ______________________________________    Display data     X      Y    ______________________________________    1                1      1    d.sub.1          X.sub.0                            Y.sub.0    d.sub.2          X.sub.0                            -Y.sub.0    0                1      -1    -d.sub.2         X.sub.0                            Y.sub.0    -d.sub.1         -X.sub.0                            -Y.sub.0    -1               -1     -1    ______________________________________

In FIG. 1, there are shown voltage values applied to a pixel withrespect to various row waveforms and column waveforms in a case that acombination of d₁ =0.6 and d₂ =0.8 in Table 1 is used. In FIG. 1, columnvoltage levels are shown in normalized form. In FIG. 1, C=2V² +2.

It is understood from FIG. 1 that for instance, gradation levels 0.8 and0.6 include commonly a pulse height of 1.4 and gradation levels 0.8 and-0.6 include commonly a pulse height of 0.2, and accordingly, fourgradation levels of ±0.6 and ±0.8 can be displayed with four levels of±1.4 and ±0.2. With addition of ±1.0, 7 gradation levels can bedisplayed with 6 levels of column voltage. In signal voltages applied ina selection time, a portion changing in column voltages is in proportionto the display data d. The RMS voltage in a non-selection time isconstant in a display frame.

In the next, attention should be paid to intervals of each gradationlevel. As is clear from the combination of gradation levels as describedabove, when the gradation data ±d₁ and ±d₂ are added for display to thedisplay data +1 and -1, the gradation levels are not formed at equalintervals. This is unadvantageous for displaying a continuous gradation.

For displaying a continuous gradation, the present invention proposesuse of the AM method in combination with another gradation method, inparticular, the FRC method, whereby the number of gradation levels canbe remarkably increased. In this case, the combination of d₁ =0.6 and d₂=0.8 in Table 1 is a special solution since data 0.6, 0.8 and 1.0 havevalues having intervals of 0.2. In other words, the gradation levelsconstitute a part of the levels formed by dividing a range of from -1 to+1 by substantially equal intervals. Specifically, ±0.2 and ±0.4 areremoved from the data having intervals of 0.2 in the range from 1 to -1.

Namely, all the gradation levels of equal intervals are not produced bythe amplitude modulation but part of the gradation levels of equalintervals are expressed. Namely, the levels are not closed by only theamplitude modulation.

In this case, with a combination of another gradation display methodsuch as FRC or PWM, the gradation levels of equal intervals can beformed while the number of gradation levels can be remarkably increased.

An example of the combination of FRC for 2 frames will be described. Forinstance, when 7 gradation levels (1, 0.8, 0.6, 0, -0.6, -0.8, -1: wherea display data 0 can be expressed by levels ±1) are displayed by usingthe AM method, and the FRC method for 2 frames are used in combination,a display of 21 gradation levels can be achieved with a scale of 0.1 inthe range from 1 to -1, by the suitable combination of the display data.The value obtained is three times as large as the case without using theFRC method.

Another example of the combination of the gradation data is described.The combination of d₁ =0.92 and d₂ =0.392 provides 25 gradation levelswhen the FRC method for 2 frames (i.e. 4 subframes) is used; 63gradation levels when the FRC method for 3 frames (i.e. 6 subframes) isused, and more than 100 gradation levels when the FRC method for 4 frame(i.e. 8 subframes) is used.

In comparison, when K₁ levels which are values having equal intervalsare displayed by the AM method, and the number of gradation levels to bedisplayed is increased by the FRC method for M frames, a display of ((K₁-1)×M+1) gradation is possible. For instance, when M is 2, a display of(2K₁ -1) gradation levels is obtainable. The number of the levels isonly less than double as a case without employing the FRC.

When a part of the gradation levels such as ±0.8, ±0.6 which areobtained by the division of a range from +1 to -1 at equal intervals istaken, and a display having a specified gradation level is displayed byusing a plurality of frames including the part of the gradation levels,a further increased number of gradation levels can be obtained incomparison with the conventional gradation displaying technique by usinga plurality of frames. And, when a part of gradation levels such as±0.92, ±0.392 having unequal intervals is used for gradation levels in asingle frame, the number of gradation levels can be drasticallyincreased as the number of frames is increased.

Table 4 shows an example of data to be put in a first frame and a secondframe in order to achieve a display of 21 gradation levels in acombination of d₁ =0.6 and d₂ =0.8 wherein 1/21 indicates an OFF voltageand 21/21 indicates an ON voltage. As described before, in accordancewith the technique that two kinds of divided data are distributed toeach of subframes, the first and second frames are respectively formedof two subframes, and the gradation levels can be expressed by usingfour subframes in total.

                  TABLE 4    ______________________________________    Gradation             1 FR     2 FR   Gradation                                      1FR    2FR    ______________________________________    21/21    -1.0    -1.0    10/21    -0.8   1.0    20/21    -1.0    -0.8     9/21    -0.6   1.0    19/21    -0.8    -0.8     8/21    0.0    0.6    18/21    -0.8    -0.6     7/21    0.0    0.8    17/21    -0.6    -0.6     6/21    0.0    1.0    16/21    -1.0    -0.0     5/21    0.6    0.6    15/21    -0.8    -0.0     4/21    0.8    0.6    14/21    -0.6    -0.0     3/21    0.8    0.8    13/21    -1.0    0.6      2/21    0.8    1.0    12/21    -1.0    0.8      1/21    1.0    1.0    11/21    0.0     0.0    ______________________________________

Table 5 shows the number of levels required for displaying 7-8 gradationlevels according to the present invention and the conventional AMmethod, and the number of gradation levels formed by combining the FRCmethod for comparison.

                  TABLE 5    ______________________________________                    Conventional                            Present                    AM method                            invention    ______________________________________    Number of voltage levels                      14        6    required    Number of gradation levels                      8         7    obtained by AM method    Number of gradation levels                      15        21    obtained by combining FRC    method for 2 frames    ______________________________________

As shown in Table 5, the conventional technique can provide only adisplay of 15 gradation levels by using 14 voltage levels. On the otherhand, the present invention can provide a display of 21 gradation levelsby using 6 voltage levels. The efficiency of gradation/level of thepresent invention is more than 3 times as large as the conventionaltechnique. This means a dramatic improvement of the quality of displayswithout a substantial increase of manufacturing cost.

Further, in accordance with the present invention, much more number ofgradation levels is obtainable with a smaller number of frames by usingtwo or more sets of gradation data. For instance, when a combination ofd₁ and d₂ in Table 1 is made double (i.e., d₁, d₂, d₁ ' and d₂ '), thenumber of voltage levels required is 10 levels, and 11 gradation levelscan be displayed in a single display frame. In this case, the number ofgradation levels can rapidly be increased as the number of frames isincreased. For instance, a display of more than 64 gradation levels canbe displayed by using the FRC method for 2 frames.

Further, in the gradation display in combination of the FRC method usingmany frames, it is effective to increase gradation levels by changingrow voltages in correspondence to the frames. In the conventionaltechnique, because a gradation display is conducted by using only theFRC method wherein signal modulation was carried out by changing rowvoltages, it was necessary to change substantially the row voltages inorder to increase the number of gradation levels (Japanese UnexaminedPatent Publication No. 230752/1994). In the conventional technique,accordingly, there were such problems that there caused a shift in biasratio (the ratio of column voltage to row voltage); the voltage ratio ofON/OFF became small and the contrast ratio and brightness were reduced.On the other hand, in the present invention, since an increase of thegradation levels due to the amplitude modulation has already beenobtained in a single frame, it is easy to further increase the gradationlevels by chaining slightly the row voltages. Accordingly, the number ofgradation levels can be increased without a substantial influence to theON/OFF voltage ratio to be applied to liquid crystal. More specifically,the conventional technique required voltage modulation of more than 100%(more than 1:2 in the row voltage ratio) among a plurality of frames,for instance. On the other hand, the present invention permits anincrease of gradation levels by a voltage modulation of less than 50%,usually less than 30%. In this case, there is no substantial effect tothe ON/OFF voltage ratio.

Application of the present invention to multiple line selection method

Description will be made as to the application of the present inventionto a multiple line selection method (including an active addressing/(AA)method) which has attracted attention recently.

In the multiple line selection method, the number of voltage levelsrequired for display is larger than that in the conventional drivingmethod even when the gradation display is unnecessary. Generally, whenan L number of lines are simultaneously selected, an (L+1) number ofvoltage levels is required.

It is especially desirable to satisfy the following two conditions inorder to apply the AM method to the multiple line selection method:

1) to reduce the number of levels required in the AM method itself aspossible, and

2) to arrange the levels used at equal intervals.

With the satisfaction of the condition 1), there is obtainablesubstantial improvement with respect to the reduction of the number ofvoltage levels in comparison with the conventional method. The reasonthat the condition 2) should be satisfied in addition to thecondition 1) is as follows.

In the multiple line selection method, since column voltages are inproportion to values obtained by matrix calculation with use of anorthogonal function of display data on the simultaneously selectedlines, many additions and subtractions are conducted between voltagelevels. In this case, if the voltage levels are not arranged at equalintervals, it is necessary to form a new level or levels according tothe respective calculations. When the number of L is large, the numberof required levels is exponentially increased. From this viewpoint, useof the display data d₁ =±0.8 and d₂ =±0.6, as intermediate gradationlevels, is suited for the multiple line selection method.

With respect to this, explanation will be made as to a case that 1, 0.8,0.6, 0, -0.6, -0.8 and -1 are used as display data for the AM method. Inthis case, in the same manner as successive line selection method, 6kinds of data, i.e., ±1, ±1.4 and ±0.2 are required as divided data Xand Y. In the multiple line selection method, column voltages aredetermined by additions and substations of these divided data. In thisexample, since it can be considered that a part of voltage levels havingintervals of 0.4 is used, the voltage levels obtained by the additionsand subtractions also have values having intervals of 0.4. Further, themaximum voltage level is 1.4.L. Accordingly, a (1.4.L/0.4)×2 number ofvoltage levels is needed in this case. On the other hand, if theoriginal voltage levels do not use a part of the levels of equalintervals, the number of required column voltage levels is exponentiallyincreased with respect to the number of simultaneously selected lines.

According to one embodiment of the present invention, the number ofvoltage levels is not exponentially increase even when a gradationdisplay is conducted by the AM method in combination of the multipleline selection method. For instance, when L=3, the number of levelsnecessary for a 7 gradation display in the AM method is only 21. Incomparison with the conventional technique, the number of levels isreduced to 1/20 or lower. Namely, in the conventional technique, errorin a display was unavoidable even with use of drivers of 8 bits, whereasin the present invention, use of drivers of 5 bits can provide a displayfree from error.

Table 6 shows an example of values of column voltage levels V_(x) andV_(y) resulted in combination of various data when three lines aresimultaneously selected (L=3), Table 6 shows voltage levels necessarywhen row selection patterns is (1,1,1) or (-1, -1, -1). All necessaryvoltage levels with respect to the all selection patterns are shown. Inthis example, the divided data produced by using the AM method aredivided into a group of ±1.4 and ±1 and a group of ±1 and ±0.2, and eachof the groups is put in each of the subframes X, Y. Namely, according tothe expression in Table 3, X₀ =1.4 and Y₀ =0.2. Thus, an increase involtage levels due to the additions and subtractions can be preventedwhen the divided data are distributed to the subframes so that datahaving the same absolute values are combined in a subframe, whereby thenumber of the divided data having different absolute values is reduced.

                  TABLE 6    ______________________________________               Voltage               Voltage    Combination of               level      Combination of                                     level    data (X)   V.sub.X    data (Y)   V.sub.Y    ______________________________________    1.4, 1.4, 1.4               ±4.2    1.0, 1.0, 1.0                                     ±3.0    1.4, 1.4, 1.0               ±3.8    1.0, 1.0, 0.2                                     ±2.2    1.4, 1.0, 1.0               ±3.4    1.0, 1.0, -0.2                                     ±1.8    1.0, 1.0, 1.0               ±3.0    1.0, 0.2, 0.2                                     ±1.4    1.4, 1.4, -1.0               ±1.8    1.0, 1.0, -1.0                                     ±1.0    1.4, 1.0, -1.0               ±1.4    1.0, 0.2, -0.2                                     ±1.0    1.4, 1.4, -1.4               ±1.4    0.2, 0.2, 0.2                                     ±0.6    1.0, 1.0, -1.0               ±1.0    1.0, -0.2, -0.2                                     ±0.6    1.0, 1.4, -1.4               ±1.0    0.2, 0.2, -0.2                                     ±2.0    1.0, 1.0, -1.4               ±0.6    1.0, -1.0, 0.2                                     ±2.0    ______________________________________

A suitable range of L is not determined by only the number of voltagelevels, but determined by an effect of controlling frame response, i.e.in consideration of the contrast ratio. The control of frame response isrelated to the number of all lines, a driving frequency, a response timeof liquid crystal and so on. For instance, when the number of all linesN is 200-400; liquid crystal has a response time (the average betweenrising time and falling time) of 150 ms or lower, and the width of theselection pulses is 20-50 μs, it is preferable that 2≦L ≦15 from theviewpoint of satisfying performance of manufacturing cost. Generally, asN is increased, the response time is faster, and the width of pulses islonger, a large L is desirable.

When the AM method is used, it is preferable to use a smaller value of Lfrom the viewpoint of the number of levels as described above, as far asthe frame response is reduced. Accordingly, the following conditions arepreferably provided.

1) When N≦300, 2≦L≦7 and

2) when N>300, 2≦L≦15.

Condition 1) is applicable to dual scan driving of the dot numbers of(H640(×RGB)×V480), (H800(×RGB)×600) or the like, or single scan drivingof a size of 1/2 or 1/4 of the dot numbers of (N=240, 300). Condition 2)is applicable to driving a picture having heavy multiplexity, forinstance, (H1024×768).

Depending on the condition of the number of simultaneously selected rowsL, there are two desirable cases: application of the divided data X andY to respective subframes, and both the divided data being used in eachof the subframes. When L is large (in particular L>4), the first case ispreferred. However, when L is small, either case may be used.

Table 6a shows an example of a combination of divided data as well asvoltage levels when L=2 and divided data X, Y are distributed torespective subframes. Table 6b shows an example of a combination ofdivided data as well as voltage levels when L=2 and divided data X, Yare used in the same subframe and the same subgroup (i.e. X data is madecorrespondence to a single row line among simultaneously selected rowsand Y data is made correspondence to another row line). In the Tables,±1.4 and ±0.2 are used as divided data X, Y.

                  TABLE 6(a)    ______________________________________              Voltage                Voltage    Combination              level        Combination                                     level    of data (X)              V.sub.X      of data (Y)                                     V.sub.Y    ______________________________________    1.4, 1.4  ±2.8      1.0, 1.0  ±2.0    1.4, 1.0  ±2.4      1.0, 0.2  ±1.2    1.0, 1.0  ±2.0      1.0, -0.2 ±0.8    1.4, -1.0 ±0.4      0.2, 0.2  ±0.4    1.4, -1.4 0            1.0, -1.0 0    1.0, -1.0 0            0.2, -0.2 0    ______________________________________

                  TABLE 6(b)    ______________________________________    Combination of Voltage    data (X,Y)     level V.sub.X    ______________________________________    1.0, 1.0       ±2.0    1.4, 0.2       ±1.6    1.4, -0.2      ±1.2    1.0, 0.2       ±1.2    1.0, -0.2      ±0.8    1.0, -1.0      0    ______________________________________

As shown in Table 6(a) and 6(b), when the data X, Y are simultaneouslymade in correspondence to lines in the same subgroup (Table 6(b)), themaximum voltage level is more reduced and at the same time, the totallevel number is more reduced. In this case, there are advantages thatthe maximum voltage of drivers can be reduced and ununiformity(crosstalk) in a display due to a waveform distortion can be be reduced.Accordingly, it is advantageous that X and Y divided data are used inthe same subgroup of the same subframe when L=2. The above-mentionedrelation is effective in particular when L is small and has an evennumber. For instance, in a case of L=2 or 4, and when X data are appliedto a half portion of simultaneously selected line and Y data are appliedto the remaining half portion, there are advantageous from the viewpointof the quality of display and the reduction of manufacturing cost.

FIG. 4 is a block diagram of an embodiment of circuit for driving aliquid crystal display device according to the multiple line selectionmethod. 6 bit digital RGB signals are stored in a memory 1 in an amountcorresponding to a single picture. Then, the digital signals are readout and are distributed, for each simultaneously selected line, to threesubframe-distribution look-up tables 2 in which the signals aresubjected to γ correction and frame distribution for frame rate control.

The frame-distributed signals output, in synchronism with subframecounters, display data for each subframe in a 3-bit parallel form. Thedisplay data are supplied to a calculation circuit 3. The signalscalculated in the circuit 3 are fed to column drivers 5 to be convertedinto column voltages, and then, the column voltages are applied to aliquid crystal display panel 7.

The calculation circuit 3 receives an orthogonal function forcalculation from a function generator 4. The orthogonal function is alsosupplied to row drivers 6 to be converted into row voltages, and then,the row voltages are applied to the liquid crystal display panel 7.Inversion signals are applied to the calculation circuit 3 and thefunction generator 4 at predetermined timing to effect the inversion ofsigns whereby a direct current component to be applied to liquid crystalis removed.

Reduction of the number of voltage levels by the determination of animaginary (dummy) row and imaginary (dummy) data

The present invention proposes that a plurality of row electrodes aresimultaneously selected; an imaginary row electrode is added to thesimultaneously selected row electrodes, and data are determined on theimaginary row electrode whereby the number of voltage levels to beapplied to data electrodes is reduced.

In one embodiment of the present invention, since gradation driving iseffected by using the AM method, display data are composed of two ormore kinds of data having different absolute values. In the following,description will be made as to conditions for reducing the number ofvoltage levels.

In one of the conditions, the display data corresponding to thesimultaneously selected row electrodes (which include at least oneimaginary electrode) are divided into plural groups of display datahaving different absolute values, and data are determined on theimaginary row electrode so that the number of display data included ineach of the groups takes a predetermined discrete integer value.

Examples of the discrete integer values are as follows: (1, 3, 5, 7, . .. ), (2, 4, 6, 8, . . . ), or (3, 6, 9, 12, . . . ).

In particularly, it is preferable that the number of the display datahaving the same absolute values in a subgroup including dummy line beunified to be an even number or an odd number in order to prevent thenumber of the imaginary electrodes becoming too much.

The above-mentioned conditions will be explained with reference to adrawing.

FIG. 2 shows the effect of reducing voltage levels in a case that asingle line of imaginary electrode is added in a driving method forselecting simultaneously two lines of row electrodes. In FIG. 2, thereare four laterally arranged columns (A) to (D), each column includingtwo cases. Explanation of each of the columns is as follows.

The column A shows a case that the number of data d₁ is unified to havean odd number, and the number of data d₂ is unified to be an evennumber. The column B shows a case that the number of data d₁ is unifiedto be an even number, and the number of data d₂ is unified to be an oddnumber. The column C shows a case that the number of data d₁ is unifiedto be an odd number and the number of data d₂ is unified to be an evennumber in the same manner as the column A, wherein, the product of datavector elements has a negative sign. The column D shows a case that thenumber of data d₁ is unified to be an even number, and the number ofdata d₂ is unified to be an odd number wherein the product of datavector elements has a negative sign.

Among the display data in FIG. 2, data in brackets indicate imaginarydata, and a waveform drawn below each of data columns is one obtained bythe data including the imaginary data. In lower columns, voltage levelsrequired to display all actual display patterns are shown inconsideration of the necessity of voltage levels having the oppositesigns in order to form an alternate current. The selection matrix shownin Table 7 is used wherein two lines are actually existing display linesare one line is an imaginary line. Further, columns in the matrixcorrespond to the time sequence of selection pulses.

                  TABLE 7    ______________________________________    1 #STR1##    ______________________________________

As shown in FIG. 2, the voltage levels required for two cases in whichthe number of data d₁ and the number of data d₂ are opposite withrespect of an even number or an odd number are respectively 8 levels.When three row electrodes are simultaneously selected, and two kinds ofdata having different absolute values are treated, 16 levels arenaturally required. In the case shown in FIG. 2, 16 levels are dividedto two cases. This can be considered that there is no level necessarilytaken since the number of respective data with respect to an even numberor an odd number is already determined. Conventionally, when two rowelectrodes are simultaneously selected, and two kinds of data havingdifferent absolute values are treated, 9 levels are required. However,when the imaginary row electrode is provided, and suitable imaginarydata are selected as proposed by the present invention, it is understoodthat voltage levels are reduced by 1 level.

Generally, when the number of display data is so determined as to have apredetermined discrete integer value, a similar effect is obtainable.However, when the number of display data is fixed to be a multiple of 3,the number of required imaginary electrodes is increased and thecontrast ratio is reduced. Accordingly, it is preferable that the numberof display data is fixed to have an even number or an odd number.

Another condition to reduce the number of voltage levels is that aselection matrix in which the sign of the product of column vectorelements is constant, is used, and data are determined on the imaginaryrow electrode so that the sign of the product of display data elementscorresponding to simultaneously selected row electrodes (including animaginary row electrode) is constant. In particular, it is preferablethat the sign of the product of the display data elements is opposite tothe sign of the product of the column vector elements of the selectionmatrix whereby the maximum voltage level can be reduced.

This condition exhibits a substantial effect to reduce the number ofvoltage levels when the number of simultaneously selected row electrodesincluding at least one imaginary row electrode is of an even number. Inspecific example concerning this condition will be explained withreference to FIG. 3.

FIG. 3 shows the effect of reducing voltage levels in a case that asingle line of imaginary electrode is added in a driving method forselecting simultaneously three lines. Bracketed data in columns ofdisplay data indicate imaginary data, and waveforms are ones obtained inthis case. In the same manner as FIG. 2, voltage levels necessary fordisplaying all actual display patterns are shown in the lowermostcolumns. The selection matrix shown in Table 8 is used wherein threelines indicate actually existing display lines, and a single linecorresponds to an imaginary line. Columns in the matrix correspond tothe time sequence of selection pulses. In this matrix, the sign of theproduct of the column vector elements is constantly negative. Forexample, although the matrix formed by inversing the sign of the columnof right end side in the matrix shown in Table 7 is also an orthogonalmatrix, such matrix does not show that the sign of the product of columnvector elements is constant.

                  TABLE 8    ______________________________________    2 #STR2##    ______________________________________

In a case shown in a column A, the number of each data d₁ or d₂ isunified to be an even number, and the sign of the product of displaydata elements is unified to be opposite to the sign of the product ofcolumn vector elements in the selection matrix. In a case shown in acolumn B, the number of each data d₁ or d₂ is unified to be an oddnumber, and the sign of the product of the display data elements isunified to be opposite to the sign of the product of the column vectorelements in the selection matrix.

In the case shown in a column C, the number of each data d₁ or d₂ isunified to be an even number, and the sign of the product of the displaydata elements is unified to be the same as the sign of the product ofthe column vector elements in the selection matrix. In the case shown ina column D, the number of data d₁ or d₂ is unified to be an even number,and the sign of the product of the display data elements is unified tobe the same as the sign of the product of the column vector elements inthe selection matrix.

As shown in FIG. 3, the numbers of voltage levels required to theabove-mentioned cases are 4, 6, 9 and 6. When 4 row electrodes aresimultaneously selected and 2 kinds of data having different absolutevalues are treated, 25 levels are originally needed. As understood fromFIG. 3, 25 levels are divided to the above-mentioned 4 cases. The reasonthat 25 levels are divided to the 4 cases is because there are levelswhich are not necessarily taken since an even number or an odd number isalready determined as to the number of respective data. Further, thepolarity inversion of data to form an alternate current waveform doesnot increase the number of voltage levels since each of the cases hasvoltage levels which are symmetrical with respect to a positive ornegative sign. The advantage that the number of voltage levels is notincreased even though the polarity inversion is conducted for analternate current form, is obtainable when the number of simultaneouslyselected rows including an imaginary row or rows is of an even number.

Further, in FIG. 3, when the sign of the product of display dataelements is opposite to the sign of the product of column vectorelements in the selection matrix, it is understood that the maximumvoltage level is decreased. It is because that there is no coincidenceof the signs of all the display data at the time of additions andsubtractions in the operation of orthogonal transformation. Use of anorthogonal matrix as a selection matrix in which the sign of the productof column vector elements is not constant, is disadvantageous in thisrespect.

As understood from FIG. 3, a case that a single line of imaginaryelectrode is added in a driving method for simultaneously selecting 3lines, provides the most preferable advantage under the conditions thatthe numbers of data d₁ and d₂ are unified to be even numbersrespectively, and the sign of the product of display data elements isunified so as to be opposite to the sign of the product of column vectorelements in the selection matrix. Namely, the most desirable conditionsfrom the viewpoints of reducing the number of voltage levels andreducing the maximum voltage levels are such that (1) the number of allsimultaneously selected lines including an imaginary electrode orelectrodes is of an even number, (2) the number of each data is unifiedto be an even number, and (3) the sign of the product of display dataelements is unified so as to be opposite to the sign of the product ofcolumn vector elements in the selection matrix.

With respect to the number of simultaneously selected row electrodes (L)in the present invention, a range of about 2≦L≦16 is desirable from theviewpoint of simplifying the structure of circuits and controlling theframe response. However, it is desirable that an orthogonal function fordetermining a series of selection pulses has a nearly square matrix soas not to increase the length of frames for completing a display fromthe viewpoint of controlling a flicker or the like. In consideration ofthis, L=2^(S) -1 is most desirable, hence, a desirable L is 3, 7 or 15.In particular, L=3 or 7 is preferable, in particular, L=3 is mostpreferable from the viewpoint of the construction of circuits anddrivers used.

As described before, when d₁ and d₂ (=(1-d₁ ²)⁰.5) are used as gradationdata, levels corresponding to APT (one line selection) are basically 6kinds: ±1, ±X₀ and ±Y₀. Accordingly, when a line of imaginary electrodeis added in the driving method for simultaneously selecting 3 lines,conditions capable of substantially reducing the number of voltagelevels are to satisfy the following items 1) to 3). However, the item 1)is not essential.

1) There are two subframes for a specified subgroup: an X subframe towhich only ±1 and ±X₀ are distributed, and an Y subframe to which only±1 and ±Y₀ are distributed;

2) The sign of the product of display data elements is unified to beopposite to the sign of the product of column vector elements in theselection matrix, and

3) The number of "±1", "±X₀ ", "±Y₀ " in the data on 4 lines should takean even number.

In the satisfaction of these conditions, the number of voltage levelscan be reduced to the lowest value. For instance, when L=3, the numberof levels required is 6 levels (±2, ±2X₀ and ±2Y₀). This is lower than1/3 in comparison with 21 levels without using imaginary data.Accordingly, the number of data bits used inside is reduced from 5 bitsto 3 bits, which permits use of an economical column driver.

The sign of the product of column vector elements in the selectionmatrix can be determined from the way how the selection matrix is formedfrom an Hadamard's matrix. Namely, when the selection matrix is formedby using an Hadamard's matrix by exchanging a row or rows or a column orcolumns, and/or inverting the polarity of a row or rows or a column orcolumns, the sign is determined depending on the number of inversion ofthe row, rows, column and columns as to whether or not the inversion isconducted even times or odd times. When the number of turns of inversionis an even number, the number of a negative sign in the data on 4 linesis rendered to be an odd number. When the number of turns of inversionis an add number, the number of a negative sign in data on 4 lines isrendered to be an even number.

Description will be made by using a 4×4 matrix in Table 8 as an example.This matrix can be obtained by treating an Hadamard's matrix as follows:

1) the second and third columns are inversed;

2) the second and third rows are exchanged, and

3) the first row is unversed.

In this case, the number of negative signs in the data on 4 lines isrendered to be an even number since the row is inverted once.

Another major advantage of the present invention is to reduce themaximum value of column voltage. A concrete explanation will be made asto a case of d₁ =0.8 and d₂ =0.6. For instance, when L=3 and data valuesare all 1.4 for the selection pulses (1, 1, 1), the column voltage levelbecomes 1.4×3=4.2. On the other hand, according to the presentinvention, the maximum value of column voltage is 1.4×2=2.8, which ishalf as in the conventional technique.

The reduction of the maximum column voltage provides not only animprovement in low power consumption rate but also suppressing a largevariation of the column voltage waveform to be applied. Namely, acrosstalk caused by a distortion of the waveform of voltages due to asudden change of the voltage (i.e., high frequency components) can bereduced.

The advantages of the present invention can be summarized as follows:

1) the number of column voltage levels can be reduced;

2) the absolute value of column voltages can be reduced; and

3) crosstalking can be reduced.

Thus, advantages of reducing manufacturing cost and improving thequality of display are simultaneously obtainable.

There is a disadvantage in the driving method wherein an imaginary lineis added because the imaginary line is added in originallysimultaneously selected lines. The disadvantage is derived from a changeof duty ratio which is caused by the fact as if there are (L+1) lineseven though only L lines are actually driven simultaneously.Specifically, the addition of an imaginary line to an L number ofsimultaneously driven lines in an N number of lines means that anN/L×(L+1) number of lines are driven.

For instance, a case of N=240 corresponds to driving 320 lines whereinthe number of simultaneously selected actual lines is 3, and animaginary electrode is added. Further, a case of N=240 corresponds todriving 280 lines wherein the number of simultaneously selected actuallines is 7, and an imaginary electrode is added. In the above-mentionedcases, the ON/OFF ratio of effective voltages are respectively 1.057 and1.062 in comparison with 1.066 in the conventional driving method.

A circuit used in a case that a dummy line is used to reduce the numberof voltage levels is substantially the same as the circuit shown in FIG.4, wherein the calculation circuit 3 corresponds to a dummy datageneration and matrix calculation look-up table having a 3 bit output.

6 bit digital LGB signals for displaying a picture are stored in amemory 1. The signals in the memory 1 are read out and supplied to threesubframe distribution look-up tables 2 for each simultaneously selectedlines. The signals are subjected to γ correction and frame distributionfor receiving frame rate control. The frame-distributed signals output,in synchronism with subframe counters, display data, as a 3 bit parallelsignal form for each subframe. The outputted display data signals aresupplied to a dummy data generation and matrix calculation look-up table(3) in which calculation is made on the display data including dummydata. The calculated signals are supplied to column drivers 5 in whichthe signals are transformed into column voltages to be applied to aliquid crystal display panel 7.

An orthogonal function is supplied for calculation from a functiongenerator 4 to the dummy data generation and matrix calculation look-uptable (3). The orthogonal function is also supplied to row drivers 6 inwhich data are transformed into row voltages to be applied to the liquidcrystal display 7. Sign-inversion signals are supplied to at apredetermined timing to the dummy data generation and matrix calculationlook-up table (3) and the function generator 4 in which operations ofinverting the signs are conducted and a direct current component appliedto liquid crystal is removed.

Reduction of ununiformity of display

When intermediate tones are displayed by the techniques which have beenexplained, a phenomenon of inversion of brightness may occur unlike theoriginal gradation levels to be displayed, depending on display patternsbecause the waveforms of column voltages have different spectrumdistributions at the time of displaying gradation data. Namely, thegradation (brightness) levels to be displayed depend on the magnitude ofthe effective voltages as well as the frequency characteristic of columnvoltages applied to a display panel. As the number of gradation levelsis increased, the difference of the effective voltages between adjoininggradation levels is slight. When the frequency characteristics of columnvoltage are different, there is a possibility of occurrence of aphenomenon of inversion of brightness between gradation levels.

One embodiment of the present invention is to solve such problem andprovides a further excellent display, and proposes that in displayingintermediate gradation data, signals which are applied to columnvoltages in response to selection pulses in a time period wherein allrow electrodes are applied with at least one selection pulsehereinbelow, (referred to as a scanning time) include in a mixed stateat least one signal which is obtained by the orthogonal transformationof a data element having the absolute value exceeding 1 among dividedgradation data and at least one signal which is obtained by theorthogonal transformation of a data element having the absolute valueless than 1. With such measures, such a disadvantage that frequencycomponents of driving signals are low in a specified gradation level canbe avoided, and the phenomenon of inversion of gradation as describedabove can be suppressed.

As mentioned before, when certain gradation data are displayed by usingthe X subframe and Y subframe, gradation data having the absolute valueexceeding 1 correspond to ±X₀ where (X₀ =d₁ +(1-d₁ ²)⁰.5) expressed inthe x subframe, and gradation data having the absolute value less than 1correspond to ±Y₀ where (Y₀ =d₁ +(1-d₁ ²)⁰.5) expressed in the Ysubframe.

Namely, the above-mentioned technique can be said that there are in amixed state column voltage levels based on divided data X and columnvoltage levels based on divided data Y in a scanning time. With suchtechnique, the waveform of column voltages is made in a high frequencyform as a whole, and the waveform of column voltages between respectivegradation levels is made uniform in terms of frequency.

As described before, in the gradation display using the AM methodaccording to the present invention, the effective voltage values tonon-selection pixels are not constant and rely on the display data undera condition that only the data of the X subframe have been finished, andthe voltage effective values to the non-selection pixels become constantregardless of the display data only when the data in the X subframe andthe Y subframe have been displayed. Accordingly, if a timing forswitching pictures is inappropriate, the effective voltages are largelyvaried, and a change of brightness in pixels is produced with a timescale to the extent visible to human eyes, whereby it is observed as avertical stripe-like ununiform portion. Such phenomenon is notable whendynamic pictures are displayed.

The present invention proposes a method for reducing such verticalstripe-like ununiform portion. Namely, when signals are applied tocolumn electrodes with respect to a simultaneously selected rowelectrode group, the signal are formed by the orthogonal transformationof all the divided gradation data necessary for displaying apredetermined gradation data, and the signals are successively applied,as a group for each of column vectors of a selection matrix, to thecolumn electrodes in response to a timing of the application ofselection pulses.

When all signals based on the divided gradation data orthogonallytransformed by a series of column vectors in the selection matrix havebeen applied, the voltage effective values applied to non-selectionpixels exhibit a constant value regardless of the display data.Accordingly, use of the above-mentioned technique can shorter the thetime period in which the voltage effective values applied to thenon-selection pixels are constant regardless of the display data, andthe occurrence of the vertical stripe-like ununiform portion can beeffectively reduced.

In the above-mentioned case that certain gradation data are displayed byusing the X subframe and the Y subframe, signals based on divided data Xand signals based on divided data Y, which are orthogonally transformedby the same column vectors in a selection matrix, are successivelyapplied, in response to a timing of applying selection pulses, to aspecified group of a simultaneously selected row electrodes. When thesignals based on the divided data X and the signals based on the divideddata Y, both having been subjected to orthogonal transformation, havebeen applied to column voltages, the voltage effective values applied tonon-selection pixels become constant regardless of the display data.

In order to explain the above-two proposals in more detail, descriptionwill be made as to selection pulse sequence in a case that a gradationdisplay is conducted by using the AM method in the present invention, ina multiple line selection method.

The relation between column electrode display pattern vectors (D) andcolumn electrode voltage sequence vectors (c) in the multiple lineselection method without using the AM method can be described as ageneral expression consisting of vectors and matrix as in Formula 7.##EQU1## (D): display pattern vectors, (c): column voltage sequencevectors, and

(S): row electrode pulse sequence matrix.

In Formula 7, the vectors (D), the vectors (c) and the matrix (S) aredefined as follows. The display pattern vectors (D)=(D₁, D₂, . . . ,D_(M)) have elements equal to the number of row electrodes M (includingan imaginary electrode or electrodes, an imaginary subgroup orsubgroups) and have display data as elements corresponding to the rowelectrodes on a specified column electrode. In the same manner asdescribed before, it is supposed that OFF indicates 1 and ON indicates-1. The column voltage sequence vectors (c)=(c₁, c₂, . . . , c_(N)) haveelements equal to the number of pulses N applied within a frame, andhave elements obtained by arranging time sequentially voltage levels toa specified column voltage in a frame.

The row electrode pulse sequence matrix (S) is a matrix of M rows and Ncolumns and have elements obtained by arranging time sequentially columnvectors composed of row electrode voltage levels with respect to aspecified column electrode in a frame. Elements corresponding tonon-selection row electrodes are made 0. The row electrode pulsesequence matrix (S) as a typical matrix can be described as in Formula 8wherein A_(i) indicates a column vector of the i th column in aselection matrix A and Z_(e) indicate a 0 vector. ##EQU2##

According to the principle of the multiple line selection method, theexchange of column vectors in the row electrode pulse sequence matrix(S) can be made as desired. Accordingly, if a specific relation betweenthe number of row electrode subgroups Ns and the number of columnvectors K in the selection matrix A can be satisfied, column vectors inthe row electrode pulse sequence matrix (S) can be exchanged withoutcausing the jumping of column vectors in the selection matrix A whereinthe jumping of column vectors may be caused in a case when a subgroup 1is selected after a subgroup Ns has been selected.

As an example, when the number of simultaneously selected row electrodes(including an imaginary electrode) is 4 and the number of column vectorsin the selection matrix A is 4, and if the number of subgroups isdetermined to be 81, there is avoidable jumping of column vectors in theselection matrix when selection moves from a subgroup 80 to a subgroup 1as shown in Formula 9. Since the elimination of the jumping minimizes anundesired low frequency component, the occurrence of a flicker can becontrolled in many cases. When the number of subgroups does not coincidewith an actually used panel, the jumping of column vectors in theselection matrix can be eliminated by providing a dummy subgroup.##EQU3##

In an AM method usable in the present invention, the voltage effectivevalues to non-selection pixels can not be constant by using a singlesubframe, and at least two subframes are required. In such AM methodapplicable to the present invention, it is necessary to apply somemodification to the above-mentioned Formula 7 in order to express therelation of the display pattern vectors (D) in a frame and the columnvoltage sequence vector (c). An example of a case that a single frame isexpressed by using two subframes X, Y will be described. In this case,(D_(X+Y)), (c_(X+Y)) and (S_(X+Y)) are used in order to distinguish themfrom (D), (c) and (S) which are for the case without using the AMmethod. Then, Formula 10 is established in the same manner as Formula 7.##EQU4##

In Formula 10, (D_(X+Y))=(D₁, D₂, . . . , D_(2M)) have elements twice asmuch as the number of row electrodes (including an imaginary electrodeor a imaginary subgroup), and have divided data X and divided data Y, aselements, which corresponds to the row electrodes on a specified columnelectrode. In convenience of explanation, the first through the M thelements and the M+1 th through the 2M th elements of (D_(X+Y)) aresupposed to be in correspondence to an M number of row electrodes on thespecified row electrodes. Further, the column voltage sequence vectors(c_(X+Y))=(c₁, c₂, . . . , c_(2N)) have elements twice as much as thenumber of pulses N applied to a subframe, and have elements which areformed by arranging time sequentially voltage levels corresponding tothe specified column electrode in a frame. (S_(X+Y)) is typicallyexpressed as shown in Formula 11 by using (S) in Formula 7 wherein Zeindicates a matrix composed of elements of 0. ##EQU5##

Namely, the row electrode pulse sequence matrix (S_(X+Y)) is a matrix of2M rows and 2N columns, and have elements formed by arranging timesequentially column vectors composed of row electrode voltage levels ona specified column electrode in a frame. The first through the M thelements and the M+1 th through the 2M th elements of (S_(X+Y))correspond to row electrodes in a panel, the row electrodes beingselected twice in a frame. Column vectors in (S_(X+Y)) correspond toelements formed by arranging time sequentially column vectors composedof row electrode voltage levels on the specified column electrode in aframe.

In the above-mentioned proposal, "signals obtained by the orthogonaltransformation of data elements having the absolute value exceeding 1among the divided gradation data and signals obtained by the orthogonaltransformation of data elements having the absolute value less than 1are included in a mixed state in signals applied to column electrodes inresponse to selection pulses in a scanning time" means that columnelectrode voltage sequence vectors (C_(X+Y)) are properly exchanged sothat column voltage levels based on divided data X and column voltagelevels based on divided data Y are mixed in the scanning time. In thiscase, the correspondent exchange of column vectors of (S_(X+Y)) areperformed.

For instance, when divided gradation data of the X subframe which areorthogonally transformed with the j th column vectors of the selectionmatrix are applied as a signal to a specified column electrode at thetime of selecting the i th simultaneously selected row subgroup, thesignal is expressed as g_(X) ^(i) _(j). Similarly, when dividedgradation data of the Y subframe which are orthogonally transformed withthe j th column vectors of the selection matrix is applied as a signalto a specified column electrode at the time of selecting the i thsimultaneously selected row subgroup, the signal is expressed as g_(Y)^(i) _(j).

When a 4 row, 4 column selection matrix is used and column voltagelevels based on divided data X are exchanged to column voltage levelsbased on divided data Y for every selection of 5 subgroups, columnelectrode voltage sequence vectors (c_(X+Y)) are expressed as shown inFormula 12, for example, where the number of subgroups is greater than5. ##EQU6##

A period for exchanging the data X and Y may be experimentallydetermined in consideration of a reduction of effective voltage due to adistortion of column voltage waveform.

"When signals are applied to the column electrodes with respect to asimultaneously selected row electrode group, the signals are formed bythe orthogonal transformation of all the divided gradation datanecessary for displaying a predetermined gradation data, and the signalsare successively applied, as a group for each of column vectors of theselection matrix, to the column electrodes in response to a timing ofthe application of the selection pulses." This means that divided data Xand divided data Y are exchanged for each selection pulse with respectto a specified simultaneously selected row electrodes. Specifically,this is a case of using the column electrode voltage sequence vectors(c_(X+Y)) as shown in Formula 13. ##EQU7##

In Formula 13, column electrode levels based on divided data X andcolumn voltage levels based on divided data X are exchanged each time of5 selection pulses.

Formula 13 shows that when the first subgroup is firstly selected, thedivided data X to the selection vector 1 is made correspondence to thefirst subgroup, and when the first subgroup is next selected (i.e. thesecond scanning), the divided data Y to the selection vector 1 is madecorrespondence to the first subgroup. Accordingly, when two times ofscanning are finished, voltage effective values on a column electrodeare constant with respect to any display pattern. This means that thevoltage effective values on the column electrode are constant in aperiod of 1/4 in comparison with a case that divided data X are madecorrespondence to four selection vectors in a subgroup, and then,divided data Y are made correspondence to four selection vectors in thesame subgroup. Accordingly, in satisfaction of two conditions: divideddata X and divided data Y for a subgroup are exchanged every selectionpulses to the subgroup, and selection vectors used for selecting thesubgroup are the same in the two scanning operations (in this case, thepolarity is not considered), a low frequency component is removed fromthe waveform of column voltages, and a smooth change of picture image isobtainable even when changes in data of a picture image are frequent ina display of dynamic picture.

Description has been made as to an example of vector sequence whereinselection vectors are changed every selection of subgroups (forinstance, the selection vectors undergo increment in a selectionmatrix). However, it is possible to use the same selection vectors inthe selection of several subgroups. The longest of the same selectionvectors is to be used for 2 subframes. This is the case that a vector 1is used for the first and second scanning, and a vector 2 is used fornext two scanning. This case substantially reduces the fundamentalfrequency of column voltage waveforms in comparison with the case thatthe vectors are changed every selection pulses as shown in Formula 13.The fundamental frequency can be adjusted by advancing periodicallyvectors every several times of selection. When the vector is advancedevery W pulses, the fundamental frequency is 1/W times as much as thecase of Formula 13.

The important items in achieving a high quality of display aresummarized as follows.

1) The number of column voltage levels necessary for gradation levels tobe displayed is appropriate (not too much), and

2) The frequency spectrum of column waveforms is not largely changeddepending on display patterns.

The item 1) indicates a condition for preventing such disadvantage thatwhen the number of column voltage levels is large, the waveform iscomplicated whereby there result crosstalking and inversion ofgradation. The item 2) is for a condition for preventing crosstalkingdue to display patterns. An embodiment according to the presentinvention provides a novel method of forming a multi-gradation displayby satisfying the above-mentioned conditions simultaneously. Namely, amulti-gradation display having high uniformity is achieved at a lowercost. The condition of 1) can be achieved by using the specifiedgradation levels as already mentioned in combination of the FRCtechnique. Further, when the multiple line selection method is used, animaginary row and imaginary data corresponding thereto are used wherebythe number of gradation levels displayed with respect to the number ofcolumn voltage levels can be further improved.

With respect to the condition 2), there are suitable waveformsynthesizing methods as follows.

2-1) Column voltage levels based on divided data X and column voltagelevels based on divided data Y are arranged in a mixed state in ascanning time. There are two kinds of technique for mixing the data X, Yin terms of a spatial size: one is to form a subgroup corresponding to Xdata and a subgroup corresponding to Y data in a scanning time, that is,mixing of units of subgroup, and the other is to distribute X data and Ydata to lines in a simultaneously selected subgroup, that is, mixing ofunits of line. For mixing, either one or both of the above-mentionedtechniques may be used.

2-2) Selection vectors used for forming selection pulses are regularlychanged in a scanning time. For instance, the selection vectors areregularly shifted in the selection matrix. The period can be changed ina range from a selection pulse to the length two scanning.

2-3) The polarity of selection vectors is inversed with a periodcorresponding to a divisor of the number of subgroups or a periodindependent of the number of subgroups. Although this technique is usedfor determining a period for forming an alternate current, it can alsocontrol the frequency spectrum of column waveforms simultaneously.

The above-mentioned three techniques can control the frequency spectrumof column waveforms independently and effectively whereby occurrence ofcrosstalking due to the fact that the column waveforms strongly rely ondisplay patterns, can be prevented. In particular, when amulti-gradation display as provided by the present invention is to berealized, a variation of voltage waveforms due to crosstalking fairlydeteriorates the quality of picture images. This tendency is remarkablein displaying dynamic pictures. The method of forming gradationaccording to the present invention can provide a picture image of highquality at a lower cost in combination with the condition of 2).

Although the technique of increasing gradation levels in combination ofthe FRC method is most desirable in the present invention as describedabove, it is possible to increase the number of gradation levels withuse of an error diffusion method or a dither method for forming agradation display by utilizing spatial information.

Further for the FRC method, it is possible to utilize a conventionalmethod. In particular, it is preferable to use a technique of spatialmodulation wherein the phase corresponding to gradation data is changedbetween adjacent pixels in a plurality of frames, whereby a change ofbrightness with respect to time can be controlled and a multi-gradationdisplay without flicker can be obtained. For instance, when 4 frames areused in the FRC method to effect a display in the present invention, thespatial modulation method may be used in combination, whereby a changeof brightness with respect to time is not substantially recognized.

Circuit structure for realizing the present invention

Description will be made as to how to form a circuit for realizing thepresent invention.

The characteristic features of the present invention are to form manygradation levels in combination of the amplitude modulation method andthe FRC method, and to form two or more divided gradation data by theamplitude modulation method to obtain column voltages. Accordingly, thebasic circuit structure of the present invention can be formed bysatisfying these points. Namely, in the basic structure of the presentinvention, there are a circuit for developing the gradation data to bedisplayed to a series of time sequentially developed gradation data, acircuit for transforming the developed gradation data (to be displayedby amplitude modulation) into divided gradation data, and a circuit fordetermining voltages to be applied to column electrodes. When themultiple line selection method is used, a circuit for forming sets ofdivided data from the gradation data to be displayed by the amplitudemodulation which correspond to subgroups consisting of simultaneouslyselected row lines; a circuit for producing selection vectors applied torow electrodes, and a circuit for determining column voltages from thesets of divided data and selection vectors. These circuits are formed oflogic circuits or ROMs. Further, some of the above-mentioned circuitsmay be formed integrally.

Gradation data are preferably stored in a memory in a form of gradationdata. It is also possible to store the original gradation data to bedisplayed into the memory whereby column voltage signals to be suppliedto a display are determined by means of the above-mentioned circuits, orto store as the gradation data to be displayed by amplitude modulationinto the memory, or to store as the divided gradation data into thememory. Among these, the most effective technique from the viewpoint ofthe size of the memory, the power consumption rate and so on is to storein the memory in the form of gradation data to be displayed by amplitudemodulation. With respect to this, several examples of the sequence aredescribed below. The above-mentioned examples 3) indicates the case ofusing multiple line selection method.

1) 8 bit gradation data→a spatial gradation forming technique (errordiffusion or dither method)→6 bit gradation data→time sequentiallydeveloping (4 frame FRC)→3 bits gradation data to be displayed by theamplitude modulation of 1 frame→memory→production of divideddata→production of column voltages→display

2) 6 bit gradation data→time sequentially developing (4 frame FRC)→3bits gradation data to be displayed by the amplitude modulation of 1frame→memory→production of divided data→production of columnvoltages→display

3) 6 bit gradation data→time sequentially developing (4 frame FRC)→3bits gradation data to be displayed by the amplitude modulation of 1frame→memory→production of divided data (plural lines)→production of lowselection pulses and column voltages (Ex-Or and addingcalculation)→display

The memory may be formed of a VRAM, a DRAM or the like as far as a widewidth of data can be obtained. As described above, it is an effectiveway to calculate the gradation data to be displayed (6 to 8 bits) inspace and time sequentially to reduce the number of bits and formamplitude modulation data of 1 frame (about 3 to 4 bits) to be stored inthe memory. Of course, it is possible to calculate directly (withoutusing memory) column voltage signals from the original gradation data.In this case, however, a large width of data and a high speed accesstime are required.

In examples 1)-3), a circuit for generating divided data is used todetermine any one of a plurality of divided data from spatialinformation on columns and rows corresponding to the spatial modulationof FRC and information on time sequence (frame counter).

The structure of the circuit will be described in more detail.

In this embodiment, a picture signal treating circuit comprises a rowselection pattern producing circuit, a frame modulation circuit fordeveloping inputted picture signals in a plurality of time sequentiallydeveloped frames, a memory capable of storing the picture signalsdeveloped in the plurality of frames (gradation data corresponding toamplitude modulation) for an amount necessary to calculate the amplitudeof voltages, a column voltage signal calculation circuit for operatingcolumn voltage signals from the picture signals from the memory and rowselection pattern signals, and a timing producing device (a device forproducing divided data X and Y) for identifying the picture signals in aspecified frame among the plurality of developed frames and addressingthe picture signals in either of the X subframe and the Y subframe.Thus, a multi-gradation display minimizing a flicker is obtainable.

Further, a frame modulation circuit which transforms picture signalsincluding gradation into a plurality of time sequentially developedframe signals before the picture signals are transferred to the memory,is used whereby a data quantity per unit time can be reduced; a displayminimizing a flicker is obtainable, and the number of memories can bereduced.

Further, the picture signal treating circuit may be formed as a integralcircuit whereby the width of data for reading and writing in the memorycan be wide and a memory having a low accessing speed (e.g. a DRAM) canbe used.

FIG. 5 shows an embodiment of the picture signal treating circuit usedfor practicing the present invention.

A picture signal treating circuit 100 comprises a frame modulationcircuit 21, an input port (shift resister), a memory (3Mbit DRAM) 23, anoutput port (shift resister) 25, a gradation data transforming circuit26, a row selection pattern producing device 27, a column voltage signalcalculating circuit 28 and a timing producing device 15.

The frame modulation circuit 21 transforms inputted gradation data ofplural bits into gradation data correspondent to the amplitudemodulation for plural frames. In this embodiment, 24 frames are used asdescribed before. The transformation of data in the frame modulationcircuit 21 is conducted by using look-up tables which correspond to fromthe first frame to the fourth frame. The transformation of data may beconducted by calculation without using the look-up tables.

The input port 22 transforms the gradation data corresponding to theamplitude modulation for frames, which are transferred from the framemodulation circuit 21 into parallel data for K pixels and transfers atone time a large amount of data to a memory at the later stage. As thevalue of K is large, an amount of data transferred at one time can belarge. In this embodiment, a shift resister is used for the input port22.

The memory 23 may be of any type as far as it has a capacity capable ofstoring data for an amount of a picture having a bit number necessaryfor calculation to form column signals at a late stage. In particular,since a picture signal treating circuit formed in an integrated form inwhich the memory is installed can store a large the width of data forreading and writing in the memory, a memory having a low access speed(e.g. a DRAM) can be used. Use of an economical DRAM is veryadvantageous in cost. Namely, in the present invention, use of the DRAMof a lower cost and a low speed is very useful from the viewpoints of alow power consumption rate and a low noise.

The output port 25 transfers data from the memory 23 to the columnvoltage signal calculation circuit 28. A shift resister is used for theoutput port in the same manner as the input port 22.

The gradation data transforming circuit 26 outputs gradation datacorresponding to the divided data X and the divided data Y by usinglogic which are previously prepared for the X subframe and the Ysubframe. The gradation data transforming circuit 26 may be formed of aselector and a logic circuit as shown in FIG. 27. The column voltagesignal calculation circuit 28 produces column signals and outputs them.The outputted data are supplied as display data to the column drivers 80in the liquid crystal display module. The row selection patternproducing device 27 produces row selection patterns based on theselection matrix. The row selection patterns are supplied to the rowdrivers 90 to form row voltages, and they also supplied to the columnvoltage signal calculation circuit 28 to be used for calculation forforming column voltage signals.

The timing producing device 15 is a control circuit which determines asto whether picture signals corresponding to a pixel are used for the Xsubframe or the Y subframe of a specified frame among a plurality ofdeveloped frames. Control signals are composed of frame signals andsignals indicating a spatial information of pixels.

Display data supplied to the column voltage signal calculation circuit28 are data arranged in the direction of column which have the samenumber as the number of simultaneously selected lines. The arrangementof the data supplied to the column voltage signal calculation circuit 28is different from the order for transforming data from a displaycontroller to the picture signal treating circuit 100.

FIG. 6 is a diagram showing the difference. FIG. 6(a) shows the order oftransferring data from the display controller to the picture signaltreating circuit 100, and FIG. 6(b) shows the order of transferring datato the column voltage signal calculation circuit 28.

Picture signals inputted to the picture signal treating circuit 100 areusually transferred successively as a set of serial data of RGB (i.e. 1pixel) so as to direct from the upper left portion of the picturesurface toward the lateral direction. When all the data on the first rowhave been transferred, the data on the second row are taken. Thus, thedata for a picture are supplied in the same manner as above.

A format for changing the order of transfer is changed at the time ofreading or writing data in the memory. For instance, when data iswritten in the memory, writing is conducted by a predetermined formatchanged with use of a random access mode, and at the time of readingout, data are continuously read out at a high speed. Or, data aresuccessively written at the time of writing, and reading is conducted bya predetermined format changed with use of the random access mode. Ineither case, the picture signal treating circuit can be formed in anintegrated form in which the memory is installed whereby the width ofdata for reading and writing can be wide. Accordingly, a sufficient timefor accessing the memory is obtainable by storing the serial data in theport so that the data can be treated as parallel data having a wide datawidth.

The operation of the circuit will be described.

The input signals from a flat panel display controller are RGB digital18 bit signals which is same as signals through an interface for TFTmodule. The picture signal treating circuit 100 also receives horizontalsynchronizing signals, vertical synchronizing signals, enabling signals,clock signals as well as data signals. The frame frequency is 60 Hz.Namely, 60 picture images are supplied in a second. 6 bit signals forRGB are inputted to the frame modulation circuit 21 in which the signalsare transformed into 3 bit×RGB output signals by using frame data (2bits) signals supplied from the timing producing device 15. In thistransformation, the 6 bit picture data undergo frame modulation withrespect to time and space. The outputted data of 23 bits×630×3×480 arewritten in the memory 23 through the input port 22.

FIG. 10 is a diagram showing an example of the structure of a memoryspace in a DRAM. The region of the DRAM is divided into 9 blocks, andthe blocks are switched by addresses control. The block size is 72×630×3(RGB)×3 bits (gradation information) in a case of VGA, or 84×800×3(RGB)×3 bits (gradation information) in a case of SVGA.

For controlling, the upper portion of the liquid crystal display panelis divided into four regions A, B, C and D, and lower portion is dividedinto four regions E, F, G and H. In the case of VGA, the A region andthe H region are respectively constituted by 24 lines, and others arerespectively constituted by 72 lines.

As shown in FIG. 10, data in the regions A to H are usually read out inparallel from 8 blocks among 9 blocks, and data of a new VGA frame arewritten in the remaining one block. In a case of using an orthogonalmatrix as a selection matrix of 4 columns, a VGA frame is constituted by8 scans since there are two subframes X, Y in the VGA frame. During 8scans, data in each block are constant, and accordingly, an voltageaveraging method can be achieved.

Signals of 3 bits RGB, i.e., 9 bits in total for the first subframeamong the first frames which undergo frame modulation are inputted tothe gradation data transforming circuit 26 via the memory 23 the outputport 25. Further, the gradation data transforming circuit 26 receivesfrom the timing producing device 15 one-bit signals which designates theX subframe or the Y subframe with respect to the corresponding to pixel(in this case, the X subframe is designates). The gradation datatransforming circuit 26 transforms the 3 bit gradation data into 2 bitgradation data depending on the designated frame X or Y (in this case, Xsubframe data). The 2 bit data correspond to ±1, ±1.4 which arementioned before as the divided data X.

The 2 bit gradation data are inputted to the column voltage signalcalculation circuit 28. To the column voltage signal calculation circuit28, 4 bit data which correspond to the first column of the orthogonalfunction from the row selection pattern producing device 27 are inputtedat the same time to select column voltages, whereby 3 bits×RGB columnvoltage data are outputted as the first scanning data.

8 times of scanning are conducted in the frame to finish one round.Usually, the frame frequency is about 60-75 Hz in which time a gradationdisplay with amplitude modulation is finished. Then, the same treatmentas above is conducted to the frame signals for the second sheet, for thethird sheet, for the fourth sheet etc. whereby one display is completed.

Description has been so made that the above-mentioned sequence is basedon the operation in synchronism with the input signals. However, it isnot always that the sequence is in synchronism with the input signals.Further, when the frequency for transferring data to the module is 60 Hzor higher, the display data are constant in one frame term of themodule, and accordingly, a voltage averaging method as the base of thepassive addressing liquid crystal driving method is established.

Thus, the driving of a video display is possible at a sufficient speed.Further, the frame modulation of data may be conducted before thewriting in the memory. The data stored in the memory can be read out insynchronism with the frame frequency of the liquid crystal modulewhereby a display with little flicker can be obtained and the number ofmemories is reduced. When the picture image treating circuit 100 of thepresent invention is formed in a form of an integrated circuit which ismounted on the circuit substrate of the LCD module of the multiple lineselection system, the interchangeability of an interface to a TFT moduleis possible. FIGS. 8 and 9 show examples of the construction of circuitin this case. FIG. 8 shows a structure comprising memories and othercircuits, and FIG. 9 shows a structure comprising elements in whichmemories are installed. Of course, the picture image treating circuitcan be mounted on the circuit substrate in a personal computer. Further,a part or the entirety of the circuit may be assembled on the chip of acolumn driver.

In FIGS. 8 and 9, explanation is made on the assumption that fullcolordigital inputs of 8 bits×3 (RGB) are used as input signals. The numberof lines simultaneously selected is 4. In the signals, two bits of alower position in the input data of each 8 bits for R, G or B are usedfor a dither treatment (a gradation method by spatial modulation), and 6bits of an upper position are used for a gradation method by framemodulation and amplitude modulation. Namely, each of the 8 bits inputdata are converted into 6 bit data in a dither circuit (DITH) andoutputted therefrom. 6 bit data are further converted into 3 bit data ina frame modulation circuit (FRC), and the 3 bit data are supplied to aninput port (WRFIFO).

The circuit shown in FIG. 8 receives as inputs data (ODD PIXEL) on thecolumn electrodes of odd number in the lateral direction of the picturesurface in parallel to data (EVEN PIXEL) on column electrodes of evennumber, whereby the operating frequency of the circuit is reduced.Accordingly, there are two circuit systems, which are identical, fortreating the data for odd numbers and even numbers. In thespecification, one of the data flow is explained. However, the otherdata flow is the same.

FIG. 8 shows such a type of circuit wherein memories are attached to theoutside of IC. An input port (WR FIFO) stores data for two pixels,namely, data of 2×3×3 (RGB)=18 bits which are supplied to memories VRAM.As the memories, there are two systems, i.e. one for data of an upperhalf (UPPER) and one for data of a lower half (LOWER), which performreading operation in parallel. Namely, data of 36 bits in total of theupper and lower half portions are simultaneously read out, and the readout data are supplied to an output port (RD FIFO) in which the data aretransformed into data on two pixels (data of 72 bits in total). Then,the data are supplied to a gradation data transforming device (XYF)which receives from a row pulse generator (RPG) one bit signal whichdesignates one of the X subframe and the Y subframe. In accordance withthe designation of either the X subframe or the Y subframe, 72 bits intotal are supplied to a column voltage signal calculation circuit (CVG).The column voltage signal calculation circuit receives row selectionpattern signals at the same time, in which column voltage signals arecalculated by using the before-mentioned input data. The calculationcircuit (CVG) outputs to liquid crystal drivers 5 bit output signals forupper and lower halves and RGB, i.e. 5×2×3=30 bit signals.

FIG. 9 shows such a type of circuit having memories included in IC(including DRAM). The major different features from the circuit in FIG.8 are that the width of data supplied to the memories is extremelylarge, and the operating speed is slow to permit use of DRAM.Accordingly, it is possible to reduce power consumption rate andmanufacturing cost. It is therefore preferable that the width of data islarge as far as IC process is possible. For instance, use of 128 bits or256 bits is effective. The bit width of the input port and output portshould be large in response to the width of data.

Now, the present invention will be described in detail with reference toexamples. However, it should be understood that the present invention isby no means restricted by such specific examples.

EXAMPLE 1

A VGA liquid crystal display panel of 480×640×RGV was prepared. Informing the display module of liquid crystal panel, 240° twisted STN wasused; phase compensation was effected with two phase compensation films;an inner color filter was combined to provide a colored display, and afluorescent tube backlight was arranged at the rear surface of thepanel. All scanning lines (selection lines) were vertically divided intotwo portions to employ a dual scan driving system. A successive linemethod (APT) was used to select each of the selection lines forgradation. Amplitude modulation was used in association-with framemodulation to thereby obtain a display of 21 gradation levels. 5 bitdata (for 32 gradation levels) were inputted. After γ correction, thedata was distributed to 21 gradation levels, and the 21 gradation levelswere distributed to 7 gradation levels for AM and frame modulation fortwo frames. The 7 gradation levels for AM were ±1, ±0.8, ±0.6 and 0correspond to the conditions: d₁ =0.8 and d₂ =0.6 in Table 1. AM dataand column voltage levels in the frames were as shown in FIG. 1 andTable 4. Each frame was divided into an X subframe and an Y subframe.The X subframe was applied with voltages corresponding to the divideddata X in Table 3, as column voltages, and the Y subframe was appliedwith voltages corresponding to the divided data Y in Table 3, as columnvoltages (where d₁ =0.8 and d₂ =0.6). The polarity of signal voltageswas inverted every 13 selection pulses.

The driving frequency was so adjusted that the width of selection pulseswas 35 μs (i.e., subframe frequency=120 Hz) and the bias ratio was 1/14.As column drivers, 8 level (3 bits) drivers were used. Row drivers wereof ordinary used 3 levels (±VR, 0).

Table 11 shows the characteristics obtained in the above-mentioneddriving method. The response time is the average time between the risingtime and the falling time. The definition is also applicable to Examples2 and 3 and Comparative Example 1.

A VGA output from a personal computer was used as an input of signalsfor driving. As a result, a display of fine gradation was obtained.Further, a display was conducted by inputting video signals in apersonal computer. As a result, a display of dynamic picture excellentin gradation was obtained although there were some residual images.

EXAMPLE 2

A VGA liquid crystal display panel was prepared in the same manner asExample 1 provided that a further high speed response type VGA panel(240° twisted film compensation type STN) of 480×640×RGB was used. Thepanel was driven as described below.

All scanning lines (selection lines) were divided vertically into twoportions to employ a dual scan driving system. A multiple line selectionmethod was used to select each three lines simultaneously. Accordingly,240 selection lines were divided into 80 subgroups, and a series ofselection pulses was determined with use of a 3×4 orthogonal matrix asshown in Table 7 so that the voltage effective values were determinedwhen each of the subgroups was selected four times.

For gradation, amplitude modulation and frame modulation were usedtogether to obtain a display of 21 gradation levels in the same manneras Example 1. 5 bit data (for 32 gradation levels) were inputted. Afterγ correction, the data were distributed to 21 gradation levels. The 21gradation level data were distributed to 7 gradation levels for AM andthe frame modulation for two frames. The 7 gradation data of AM were ±1,±0.8, ±0.6 and 0 which are correspond to the condition of d₁ =0.8 and d₂=0.6 in Table 1. The AM data and the column voltage levels in the frameare shown in Table 4. The AM 7 gradation data were d₁ =0.8 and d₂ =0.6which were distributed to the X subframe and the Y subframe as shown inTable 3.

The polarity of data signals was inverted after two frames (4 subframes)have been completed. The X subframe was applied with voltage levelsobtained by calculating the divided data X in Table 3, as columnvoltages, and the Y subframe was applied with voltage levels obtained bycalculating the divided data Y in Table 3, as column voltages.

The driving frequency was so adjusted that the width of selection pulseswas 35 μs (i.e., subframe frequency=120 Hz), and the maximum bias ratio(row voltage/maximum column voltage) was 1/5. As column drivers, 32level (5 bits) drivers were used (in this case, 20 levels were used),and row drivers were of ordinary used 3 levels (±V_(R),0).

Table 11 shows the characteristics obtained by using the above-mentioneddriving method.

A VGA output from a personal computer was used as a signal input fordriving. As a result, a display of fine gradation was obtained. Further,video signals were inputted to a personal computer for display. As aresult, a display of dynamic picture excellent in gradation and freefrom residual images could be obtained.

Further, in either a display of static picture by the windows or adisplay of dynamic picture using video signals, an excellent display ofpicture images was obtained, which was of higher contrast ratio and lesscrosstalking than Example 1.

Further, when 6 bit (64 gradation levels) data were used as an input,and the 6 bit data are distributed to the frame modulation for 4 framesand the AM modulation for 7 gradation levels, a display of 41 gradationlevels could be obtained.

EXAMPLE 3

The same liquid crystal display panel as in Example 1 was used. Indriving, column voltage levels as specified in Table 9 were used.Namely, 7 display data: 1, 0.866, 0.5, 0, -0.5, -0.866 and -1 were used.

                  TABLE 9    ______________________________________    AM gradation  Divided data X                             Divided data Y    ______________________________________    1             1          1    2             1.366      0.366    3             1.366      -0.366    4             1          -1    5             -1.366     0.366    6             -1.366     -0.366    7             -1         -1    ______________________________________

The characteristics obtained for the module are shown in Table 11.

The 21 gradation levels in the two frames had no equal intervals.

The number of input bits was changed to 6 bits (64 gradation levels) andthe 64 bit data are distributed to the frame modulation for 4 frames andthe AM modulation for 7 gradation levels. In conducting a display, agradation display having equal intervals was obtained and the number ofgradation was 61.

Comparative Example 1

The same VGA liquid crystal display panel of 480×640×RGB (240° twistedfilm compensation type STN) as in Example 1 was driven in the followingmanner.

All scanning lines (selection lines) were vertically divided into twoportions to employ a dual scan driving system. A successive line method(APT) was used to select each line of selection lines. For gradation,the amplitude modulation and the frame modulation were used together toeffect a display of 15 gradation levels. In displaying gradation, 4 bitdata (for 16 gradation levels) were inputted to be distributed to 15gradation levels. The 15 gradation level data were distributed to 8gradation levels for AM the frame modulation for 2 frames. The 8gradation levels by the AM modulation were composed of numerical valueshaving equal intervals in a range between a display data -1 (ON) and adisplay data +1 (OFF).

The polarity of data signals was inverted every 13 selection pulses.Each of the frames was divided into the X subframe and the Y subframewherein the X subframe was applied with voltages corresponding to thedivided data X and the Y subframe was applied with voltagescorresponding to the divided data Y. The driving frequency was so formedthat the width of selection pulses was 35 μs (i.e., subframefrequency=120 Hz) and the bias ratio was 1/14.

The characteristics obtained by the above-mentioned driving method areshown in Table 11.

As column drivers, 16 level (4 bits) drivers were used wherein 14 levelswere used, and as row drivers, ordinary used three level (±V_(R), 0) rowdrivers were used.

A VGA output from a personal computer was used as an signal input fordriving. As a result, a display of fine gradation was obtained. Further,when video signals were input to a personal computer for display, adisplay of dynamic picture with slight residual images could beobtained. However, the quality of the display was lower than those inExamples 1, 2 and 3.

Table 9 shows the number of column voltage levels and number ofgradation levels concerning the above-mentioned Examples and ComparativeExample.

                  TABLE 10    ______________________________________           Column  Driving   2 frame   4 frame           voltage method    gradation gradation    ______________________________________    Example 1             6 levels  APT       21      41                                 gradation                                         gradation    Example 2             20 levels multiple  21      41                       line      gradation                                         gradation                       selection    Example 3              6 levels APT       21      61                                 gradation                                         gradation    Comparative             14 levels APT       15      29    Example 1                    gradation                                         gradation    ______________________________________

                  TABLE 11    ______________________________________                                      Comparative    Example 1     Example 2 Example 3 Example 1    ______________________________________    Contrast            30:1      50:1      30:1    30:1    ratio    Response            150 ms    70 ms     150 ms  150 ms    time    ______________________________________

EXAMPLE 4

A VGA liquid crystal display panel of 480×640×RGB was prepared. Informing the display module of the liquid crystal display panel, a 240°twisted STN was used; phase compensation was effected with two sheets ofphase compensation films; an inner filter was combined to obtain acolored display, and a fluorescent tube backlight was disposed at therear surface.

All scanning lines (selection lines) were vertically divided into twoportions for dual scan driving. A multiple line selection method wasused to select three lines simultaneously for driving. Accordingly, 240selection lines were divided into 80 subgroups. A series of selectionpulses was determined with use of the 4×4 orthogonal matrix as shown inTable 8. A single imaginary line was provided in each of the subgroupsso that four lines was simultaneously selected imaginarily for driving.

For gradation, amplitude modulation and frame modulation were usedtogether to obtain a display of 21 gradation levels. 5 bit data (32gradation levels) were inputted. After γ correction, the data weredistributed to 21 gradation levels, and the 21 gradation level data weredistributed to 7 gradation levels for AM and the frame modulation for 2frames. The 7 gradation data displayed by AM were ±1, ±0.8, ±0.6 and 0.The display data were distributed for each of the frames by the framemodulation as shown in Table 4. Further, the 7 gradation data by AM weredistributed to the X subframe and the Y subframe.

Imaginary data on the imaginary lines were calculated with use of thedata on actual three lines by using the following three conditions, andcalculations on the matrix were effected in accordance with signals froma row (selection) function generator to thereby obtain column voltagelevels corresponding to selection pulses of 6 levels. The obtained datawere transferred as 3 bit signals to column drivers.

Condition 1: In subframes having an odd number, data ±1, ±1.4 were usedas divided data X for 1 line, and in subframes having an even number,±1, ±0.2 were used as divided data Y for 1 line.

Condition 2: Data on imaginary lines are so determined that the numberof ±1 as the divided data for four lines has an even number.

Condition 3: Data on imaginary lines are so determined that the numberof a negative sign on the divided data for four lines has an evennumber.

The polarity of data signals was inverted after operations to two frames(4 subframes) have been finished. Column voltages obtained by thecalculation of the divided data X in Table 3 were applied to the Xsubframe, and column voltages obtained by the calculation of the divideddata Y in Table 3 were applied to the Y subframe.

The driving frequency was so determined that the width of selectionpulses was 35 μs (i.e., subframe frequency=120 Hz) and the maximum biasratio (row voltage/maximum column voltage) was 1/5. For column drivers,8 level (3 bit) drivers were used (actually 6 levels were used), andordinary three levels (±V_(R), 0) were used for row drivers.

In the characteristics obtained by the above-mentioned driving method,the contrast ratio was 40:1 and the response time (average) was 70 ms.

A VGA output from a personal computer was used as a signal input. As aresult, a display having fine gradation was obtained. Further, whenvideo signals were input to a personal computer to display the signaldata, a display of dynamic pictures having excellent gradation wasobtained while there was few residual images.

In either display of static pictures by windows or display of dynamicpictures using video signals, excellent picture images were obtained anda display having a high contrast ratio while minimizing crosstalking wasobtained.

Further, 6 bit data (64 gradation levels) were used as input data, andthe data were distributed to frame modulation for four frames and AMmodulation for 7 gradation levels. When the data were displayed, adisplay having 41 gradation levels was obtained.

EXAMPLE 5

In the same manner as Example 4, the liquid crystal display element wasdriven provided that the selection matrix as shown in Table 12 was used.

                  TABLE 12    ______________________________________    3 #STR3##    ______________________________________

The manner of determining imaginary data was partially changed inaccordance with a change of the selection matrix. Namely, the data onimaginary lines were so determined that the number of negative signs ondivided data for four lines had an odd number although the number ofnegative signs on the divided data for four lines had an even number inthe condition 3 of Example 4.

The characteristics of the module obtained were the same as those inExample 4, and substantially the same quality of picture images as inExample 4 was obtained.

EXAMPLE 6

In Example 4, an imaginary subgroup was added so that the number ofsubgroups was 81 and the jumping sequence of column vectors in theselection matrix was eliminated. In this case, the polarity of datasignals was inversed every 13 selection pulses. Further, the 7 gradationdata by AM and FRC for 2 frames were used together, and the AM data weredispersed with respect to space and time in order to prevent occurrenceof a flicker. Specifically, the data expressed in the first frame andthe second frame were divided to pixels of 2×2 on the display surface,as shown in Table 13.

                  TABLE 13    ______________________________________    1 FR                    2 FR    ______________________________________    1       2               2     1    1       2               2     1    ______________________________________

Further, the divided data X was exchanged to the divided data Y everyselection of 5 subgroups in a scanning time. Namely, the column voltagesequence vectors (c_(X+Y)) as shown in Formula 12 were used.

With use of the above-mentioned technique, crosstalking in a half tonearea was remarkably reduced. Further, a phenomenon of inversion ofbrightness to the original gradation levels (effective voltage levels)was substantially suppressed.

EXAMPLE 7

The same technique of driving as shown in Example 6 was taken exceptthat signals based on the divided data X and divided data Y which wereformed by the orthogonal transformation with the same column vectors inthe selection matrix were successively applied to specified rowelectrode groups, each of which were simultaneously selected, inresponse to a timing of selection pulses. Namely, the column voltagesequence vectors (c_(X+Y)) were used.

By using such technique, a vertical stripe-like uneven portion in adynamic picture which occurred in AM was greatly reduced. As a result,when a display was effected with video signals, a display of excellentquality was obtained while there was little crosstalking.

EXAMPLE 8

A VGA liquid crystal display panel of 480×640×RGB was prepared. Thedisplay module of the liquid crystal panel was formed as follows. A 240°twisted STN was used: phase compensation was effected with two sheets ofphase compensation films; an inner color filter was combined to obtain acolored display, and a fluorescent tube backlight was disposed at therear surface.

All scanning lines (selection lines) were vertically divided into twoportions for dual scan driving. A multiple line selection method wasused to select two lines simultaneously. Accordingly, 240 selectionlines were divided to 120 subgroups. A series of selection pulses wasdetermined with use of a 2×4 orthogonal matrix based on two 2×2orthogonal matrices as shown in Table 14. Accordingly, with respect toON and OFF data, the effective voltage values were fixed when each ofthe subgroups has been selected twice, and with respect to data ofintermediate tones, the effective voltage values were fixed when each ofthe subgroups was selected 4 times.

                  TABLE 14    ______________________________________    4 #STR4##    ______________________________________

The reason why the vectors as in Table 14 is used is that frequencycomponents in the row waveforms between simultaneously selected two rowlines are made equal, whereby the uniformity of voltages in thedirection of rows can be obtained. In the above matrix, columns(selection vectors) from the left side to the right side are calledA1-A4 respectively.

For gradation, amplitude modulation and frame modulation were usedtogether to effect a display of 21 gradation levels. 5 bit data (32gradation levels) were input. After γ correction, the data weredistributed to 21 gradation levels, and the 21 gradation data aredistributed to 7 gradation levels by AM and frame modulation for 2frames. Data ±1, ±0.8, ±0.6 and 0 were used for 7 gradation levelsdisplayed by AM. The display data as shown in Table 4 were distributedto the frames by the frame modulation. Further, the 7 gradation data byAM were divided for display to X data and Y data as divided data.

The relation of the X data or the Y data to scanning operations inspecified frames depended on subgroups. The X data were used for thefirst scanning for the first to the 5 th subgroups, and the X data wereused for the first scanning for the next 5 subgroups. Further, the Xdata were exchanged with the Y data in the next scanning.

In this case, the selection vectors used for the first scanning weremade equal to those in the second scanning, and selection vectors usedin the third scanning were made equal to those in the fourth scanning sothat the selection vectors were changed every two scanning. Further, theselection vectors were regularly changed every 3 turns of selection sothat there was a series of selection vectors, A1, A1, A1, A2, A2, A2,A3, A3, A3, . . . , in the first and second scanning, and there was aseries of selection vectors, A2, A2, A2, A3, A3, A3, . . . , in thethird and fourth scanning. The selection vectors and the divided data asshown in Table 15 are applied to the first subgroup in the respectivescanning.

                  TABLE 15    ______________________________________    Frame    Scanning       Selection                                     Divided    number   number         vector   data    ______________________________________    1st frame             1st scanning   A1       X             2nd scanning   A1       Y             3rd scanning   A2       X             4th scanning   A2       Y    2nd frame             1st scanning   A3       X             2nd scanning   A3       Y             3rd scanning   A4       X             4th scanning   A4       Y    ______________________________________

The polarity inversion was made every 31 pulses independent of theabove-mentioned sequence.

Column signals were obtained by calculating the selection vectors andthe divided data. As column drivers, 4 bit (16 level) drivers were used.

In the characteristics obtained in the above-mentioned driving method,the contrast ratio was 35:1 and the response time (average) was 70 ms.

A VGA output from a personal computer was used as a signal input. As aresult, a display of fine gradation was obtained. Further, video signalswere input for display to a personal computer. As a result, a display ofdynamic pictures excellent in gradation could be obtained while therewas substantially no residual images.

In either of a display of static pictures by windows or a display ofdynamic picture using video signals, excellent picture images wasobtained, and a display having a high contrast ratio and littlecrosstalking could be obtained.

Further, 6 bit (64 gradation levels) data were distributed to framemodulation for 4 frames and AM modulation for 7 gradation levels. Indisplaying the data, a display of 41 gradation levels could be obtained.

EXAMPLE 9

Picture images were displayed by using substantially the same drivingmethod as example 8 except that the exchange of the X data and Y datawere done in the subgroups and between subgroups. Further, dummysubgroups were inserted into exchanged portions of X and Y data betweensubgroups, and data on the next subgroups were used as imaginary data onthe electrodes in the dummy subgroups, whereby unevenness of brightnessbetween subgroups due to a distortion of the waveforms which mightresult from the exchange of X and Y data in the subgroups could beremoved. The exchange of the X and Y data between the subgroups wasconducted every 20 subgroups. For this, all the subgroups were dividedinto 6 blocks, and 6 dummy subgroups (12 imaginary lines) were provided.

In the first scanning for the first frame in the first block, the X datawere distributed to the first line and the Y data were distributed tothe second line, wherein the first and the second lines weresimultaneously selected. In the second block, the Y data weredistributed to the first line and the X data were distributed to thesecond line. In the next scanning, the X and Y data were exchanged.

The driving duty was 1/252. However, substantially the samecharacteristics as in Example 8 could be obtained, and picture imageshaving high uniformity could be obtained.

EXAMPLE 10

Picture images were displayed by using substantially the same drivingmethod as in Example 8. However, for gradation, two kinds of gradationdata set corresponding to amplitude modulation, which were timesequentially developed by FRC were used. A display of gradation data waseffected in such a manner that for column lines having an odd number,gradation data A were used for odd number frames while gradation data Bwere used for even number frames, and for column lines having an evennumber, gradation data B were used for odd number frames while gradationdata A were used for even number frames. A(1, 0.8,0.6,0,-0.6,-0.8,-1)and B (1,0.88,0.47,0,-0.47,-0.88,-1) were used for the gradation data Aand B. With use of FRC for 2 frames, a display having more than 40gradation levels could be obtained. The number of gradation levels wasgreatly increased in comparison with 21 gradation levels which wasobtained by using only the gradation data A. In this example, 5 bitcolumn drivers were used wherein 27 levels were used.

EXAMPLE 11

Picture images were displayed by using substantially the same drivingmethod as in Example 8.

As gradation data for one frame, (1,0.8,0.6,0,-0.6,-0.8,-1) were used. Agradation display was conducted by changing the absolute value of theamplitude of row voltages between odd number frames and even numberframes. In this case, the row voltages in the even number frames weredetermined to be 0.75 times as much as those of the odd number frames.

Substantially the same contrast as in Example 8 could be obtained. Adisplay of 44 gradation levels was obtained with 2 frames and a displayof more than 100 gradation levels was obtained with 4 frames.

In accordance with the present invention, gradation driving utilizingamplitude modulation is possible while the number of levels for columndrivers is maintained in 20 a realistic range of level (64-32 levels orlower).

Namely, a gradation display free from a flicker, simplification of thecircuit system and reduction of manufacturing cost can be achieved.

Further, a display can be effected independently without data error. Apicture image of high quality can be presented without a specialtreatment of data. Namely, a picture image can be obtained withoutinformation error such as crosstalking.

Further, the maximum level of column voltages can be controlled to below whereby power consumption rate can be reduced; a change of voltagewhich may cause an ununiformity of display is made small, and a displayof high quality can be obtained.

The present invention is very effective for the multiple line selectionmethod.

We claim:
 1. A driving method for a liquid crystal display device havingaccessible display portions forming pixels, using a multiplex drivingmethod which comprises:applying to said pixels groups of voltage pulseshaving respective group pulse heights which vary in at least twodifferent groups depending on gradation levels of data to be displayed,at least two of said respective group pulse heights having a differentabsolute magnitude in at least one of the at least two of the groupswith the respective group pulse heights in the groups includingcomponents having a value such that RMS voltages applied to said pixelson scanning electrodes in a non-selection state are effectively madeconstant in a display frame period, and using at least one common pulseheight in the at least two of the groups, whereby the number of pulseheights used in all of the groups to cause display of all desiredgradation levels is reduced.
 2. A driving method according to claim 1,further comprising the step of displaying said gradation levels inassociation with a frame modulation or a pulse width modulation.
 3. Adriving method according to claim 1 further comprising simultaneouslyselecting a plurality of scanning electrodes and applying displayinducing pulses to the selected scanning electrodes defined by aselection matrix having a substantial orthogonality.
 4. A driving methodaccording to claim 3, further comprising adding at least one imaginaryscanning electrode to the simultaneously selected scanning electrodes,and determining data for the imaginary scanning electrode so that thenumber of voltage levels to be applied to data electrodes is reduced. 5.A driving method for a liquid crystal display device having accessibledisplay portions forming pixels, and using a multiplex driving methodwhich comprises:applying to said pixels groups of voltage pulses,wherein at least one of the groups has at least two pulses withdifferent absolute magnitude pulse heights, wherein each of the groupscorrespond to one of a plurality of achievable display gradation datalevels provided as including components having variable levels such thatRMS voltages applied to said pixels on scanning electrodes in anon-selection state are effectively made constant in a display frameperiod, and using a part of the divided gradation data commonly relativeto at least the at least two groups to provide at least two differentdisplay gradation data levels for display.
 6. A driving method accordingto claim 5, further comprising displaying said display gradation datalevels in association with a frame modulation or a pulse widthmodulation.
 7. A driving method according to claim 5, further comprisingobtaining said display gradation data levels in at least said at leasttwo groups as at least two voltage pulses including pulse heights whichvary depending on the display gradation data levels to be displayed andcorrespond to at least a part of a range of levels from -1 to +1 dividedinto substantially equal intervals.
 8. A driving method according toclaim 5, wherein said gradation data levels d span a range from -1,which indicates ON, to 1, which indicates OFF, said gradation datalevels being effectively displayed by displaying first and seconddivided gradation data d±√1-d² .
 9. A driving method according to claim5, wherein a plurality of scanning electrodes are simultaneouslyselected, and pulses applied to the selected scanning electrodes aredefined by a selection matrix having a substantial orthogonality.
 10. Adriving method according to claim 9, wherein the data electrodescorresponding to the simultaneously selected scanning electrodes areapplied with signals which are obtained by transforming the dividedgradation data with said selection matrix.
 11. A driving methodaccording to claim 9, wherein said gradation data levels d span a rangefrom -1, which indicates ON, to 1, which indicates OFF, said gradationdata levels being effectively displayed by displaying first and seconddivided gradation data d±√1-d² gradation data ±d√-1-d² , wherein.
 12. Adriving method according to claim 11, wherein when the intermediategradation data are displayed, signals which are applied to the dataelectrodes in response to selection pulses in a time period wherein allthe scanning electrodes are applied with at least one selection pulseinclude in a mixed state at least one signal which is obtained by theorthogonal transformation of a data element having the absolute valueexceeding 1 among the divided gradation data and at least one signalwhich is obtained by the orthogonal transformation of a data elementhaving the absolute value less than
 1. 13. A driving method according toclaim 11, wherein when the intermediate gradation data are displayed,signals which are applied to the data electrodes in response toselection pulses applied once to a simultaneously selected scanningelectrode group include in a mixed state at least one signal which isobtained by the orthogonal transformation of a data element having theabsolute value exceeding 1 among the divided gradation data and at leastone signal which is obtained by the orthogonal transformation of a dataelement having the absolute value less than
 1. 14. A driving methodaccording to claim 9, wherein when signals are applied to the dataelectrodes with respect to a simultaneously selected scanning electrodegroup, the signals are formed by the orthogonal transformation of allthe divided gradation data necessary for displaying a predeterminedgradation data, and the signals are successively applied as a group foreach of column vectors of the selection matrix, to the column electrodesin response to a timing of the application of the selection pulses. 15.A driving method according to claim 9, wherein at least one imaginaryscanning electrode is added to the simultaneously selected scanningelectrodes, and data are determined for the imaginary scanning electrodeso that the number of voltage levels to be applied to data electrodes isreduced.
 16. A driving method according to claim 15, wherein the displaydata corresponding to the simultaneously selected scanning electrodes,which include at least one imaginary scanning electrode are divided intoplural groups of display data having different absolute values; and dataare determined for the at least one imaginary scanning electrode so thatthe number of display data included in each of the groups takes apredetermined discrete integer value.
 17. A driving method according toclaim 15, wherein the product of the column vector elements in theselection matrix takes a predetermined sign, and data are determined forthe imaginary scanning electrodes so that the product of the displaydata elements corresponding to the simultaneously selected scanningelectrodes, which include at least one imaginary scanning electrode,takes a predetermined sign.
 18. A method for driving a liquid crystaldisplay device so that the number of voltage levels applied to dataelectrodes is reduced, comprising:simultaneously selecting a pluralityof scanning electrodes; applying signals to data electrodescorresponding to the simultaneously selected scanning electrodes, saidsignals being obtained by transforming gradation data with asubstantially orthogonal selection matrix, the gradation data beingcomposed of at least two kinds of data elements having differentabsolute values; adding at least one imaginary scanning electrode to thesimultaneously selected scanning electrodes; determining gradation datafor the at least one imaginary scanning electrode to be one of the atleast two kinds of data elements and the number of each data elementbeing one of a predetermined discrete integer.
 19. A driving methodaccording to claim 18, wherein a product of column vector elements inthe selection matrix has predetermined sign, and data are determined forthe at least one imaginary scanning electrode so that the product of thedisplay data elements corresponding to the simultaneously selectedscanning electrodes and the at least one imaginary scanning electrodehas a predetermined sign.